Re: [PATCHv5] gpio: Remove VLA from gpiolib
On 15/05/2018 15:10, Geert Uytterhoeven wrote: Hi Laura, On Tue, May 15, 2018 at 12:49 AM, Laura Abbott wrote: On 04/20/2018 02:02 AM, Geert Uytterhoeven wrote: On Fri, Apr 13, 2018 at 11:24 PM, Laura Abbott wrote: The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Blindly replacing VLAs by allocated arrays is IMHO not such a good solution. On the largest systems, NR_GPIOS is 2048, so that makes 2 arrays of 256 bytes. That's an uppper limit, and assumes they are all on the same gpiochip, which they probably aren't. Still, 2 x 256 bytes is a lot, so I agree it should be fixed. So, wouldn't it make more sense to not allocate memory, but just process the request in chunks (say, at most 128 gpios per chunk, i.e. 2 x 16 bytes)? The code already caters for handling chunks due to not all gpios belonging to the same gpiochip. That will probably also be faster than allocating memory, which is the main idea behind this API. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); FWIW, can this warning be triggered from userspace? @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; Hence just use a fixed size here... + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); Out-of-context, the code does: | __set_bit(hwgpio, mask); | i++; | } while ((i < array_size) && ... and change this limit to "(i < min(array_size, first + ARRAY_SIZE(mask) * BITS_PER_BYTE))" | (desc_array[i]->gdev->chip == chip)); ... and you're done? I don't think this approach will work since gpio_chip_{get,set}_multiple expect to be working on arrays for the entire chip. There doesn't seem to be a nice way to work on a subset of GPIOs without defeating the point of the multiple API. You're right, sorry for missing that. is 2*256 = 512 bytes really too much stack space? I guess we could switch to a Kconfig to allow for better bounds. That's a good question. As long as a VLA is used, it's probably fine, as chip->ngpio is quite small. If you would change it to an array that can accommodate NR_GPIOS bits, you have to start caring about recursion (e.g. gpio-74x164 driven from spi-gpio, where I can extend the chain to increase the level of recursion arbitrarily). I think a config option for FASTPATH_NGPIO is preferable. As I've mentioned ARCH_NR_GPIOS is much greater than any chip->ngpio on my platform. It's at least one order of magnitude, almost 2. -- Regards Phil Reid
Re: [PATCHv5] gpio: Remove VLA from gpiolib
Hi Laura, On Tue, May 15, 2018 at 12:49 AM, Laura Abbott wrote: > On 04/20/2018 02:02 AM, Geert Uytterhoeven wrote: >> On Fri, Apr 13, 2018 at 11:24 PM, Laura Abbott wrote: >>> The new challenge is to remove VLAs from the kernel >>> (see https://lkml.org/lkml/2018/3/7/621) to eventually >>> turn on -Wvla. >>> >>> Using a kmalloc array is the easy way to fix this but kmalloc is still >>> more expensive than stack allocation. Introduce a fast path with a >>> fixed size stack array to cover most chip with gpios below some fixed >>> amount. The slow path dynamically allocates an array to cover those >>> chips with a large number of gpios. >> >> >> Blindly replacing VLAs by allocated arrays is IMHO not such a good >> solution. >> On the largest systems, NR_GPIOS is 2048, so that makes 2 arrays of 256 >> bytes. That's an uppper limit, and assumes they are all on the same >> gpiochip, >> which they probably aren't. >> >> Still, 2 x 256 bytes is a lot, so I agree it should be fixed. >> >> So, wouldn't it make more sense to not allocate memory, but just process >> the request in chunks (say, at most 128 gpios per chunk, i.e. 2 x >> 16 bytes)? The code already caters for handling chunks due to not all >> gpios >> belonging to the same gpiochip. That will probably also be faster than >> allocating memory, which is the main idea behind this API. >> >>> Reviewed-and-tested-by: Lukas Wunner >>> Signed-off-by: Lukas Wunner >>> Signed-off-by: Laura Abbott >> >> >>> --- a/drivers/gpio/gpiolib.c >>> +++ b/drivers/gpio/gpiolib.c >> >> >>> @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip >>> *chip, void *data, >>> goto err_free_descs; >>> } >>> >>> + if (chip->ngpio > FASTPATH_NGPIO) >>> + chip_warn(chip, "line cnt %d is greater than fast path >>> cnt %d\n", >>> + chip->ngpio, FASTPATH_NGPIO); >> >> >> FWIW, can this warning be triggered from userspace? >> >>> @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool >>> can_sleep, >>> >>> while (i < array_size) { >>> struct gpio_chip *chip = desc_array[i]->gdev->chip; >>> - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; >>> - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; >> >> >> Hence just use a fixed size here... >> >>> + unsigned long fastpath[2 * >>> BITS_TO_LONGS(FASTPATH_NGPIO)]; >>> + unsigned long *mask, *bits; >>> int first, j, ret; >>> >>> + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { >>> + memset(fastpath, 0, sizeof(fastpath)); >>> + mask = fastpath; >>> + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); >>> + } else { >>> + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), >>> + sizeof(*mask), >>> + can_sleep ? GFP_KERNEL : >>> GFP_ATOMIC); >>> + if (!mask) >>> + return -ENOMEM; >>> + bits = mask + BITS_TO_LONGS(chip->ngpio); >>> + } >>> + >>> if (!can_sleep) >>> WARN_ON(chip->can_sleep); >>> >>> /* collect all inputs belonging to the same chip */ >>> first = i; >>> - memset(mask, 0, sizeof(mask)); >>> do { >>> const struct gpio_desc *desc = desc_array[i]; >>> int hwgpio = gpio_chip_hwgpio(desc); >> >> >> Out-of-context, the code does: >> >> | __set_bit(hwgpio, mask); >> | i++; >> | } while ((i < array_size) && >> >> ... and change this limit to "(i < min(array_size, first + >> ARRAY_SIZE(mask) * BITS_PER_BYTE))" >> >> | (desc_array[i]->gdev->chip == chip)); >> >> ... and you're done? >> > I don't think this approach will work since gpio_chip_{get,set}_multiple > expect to be working on arrays for the entire chip. There doesn't seem > to be a nice way to work on a subset of GPIOs without defeating the point > of the multiple API. You're right, sorry for missing that. > is 2*256 = 512 bytes really too much stack space? I guess we could > switch to a Kconfig to allow for better bounds. That's a good question. As long as a VLA is used, it's probably fine, as chip->ngpio is quite small. If you would change it to an array that can accommodate NR_GPIOS bits, you have to start caring about recursion (e.g. gpio-74x164 driven from spi-gpio, where I can extend the chain to increase the level of recursion arbitrarily). Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journ
Re: [PATCHv5] gpio: Remove VLA from gpiolib
On 04/20/2018 02:02 AM, Geert Uytterhoeven wrote: Hi Laura, Thanks for your patch! On Fri, Apr 13, 2018 at 11:24 PM, Laura Abbott wrote: The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Blindly replacing VLAs by allocated arrays is IMHO not such a good solution. On the largest systems, NR_GPIOS is 2048, so that makes 2 arrays of 256 bytes. That's an uppper limit, and assumes they are all on the same gpiochip, which they probably aren't. Still, 2 x 256 bytes is a lot, so I agree it should be fixed. So, wouldn't it make more sense to not allocate memory, but just process the request in chunks (say, at most 128 gpios per chunk, i.e. 2 x 16 bytes)? The code already caters for handling chunks due to not all gpios belonging to the same gpiochip. That will probably also be faster than allocating memory, which is the main idea behind this API. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); FWIW, can this warning be triggered from userspace? @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; Hence just use a fixed size here... + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); Out-of-context, the code does: | __set_bit(hwgpio, mask); | i++; | } while ((i < array_size) && ... and change this limit to "(i < min(array_size, first + ARRAY_SIZE(mask) * BITS_PER_BYTE))" | (desc_array[i]->gdev->chip == chip)); ... and you're done? I don't think this approach will work since gpio_chip_{get,set}_multiple expect to be working on arrays for the entire chip. There doesn't seem to be a nice way to work on a subset of GPIOs without defeating the point of the multiple API. is 2*256 = 512 bytes really too much stack space? I guess we could switch to a Kconfig to allow for better bounds. Thanks, Laura @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip *chip, } } -void gpiod_set_array_value_complex(bool raw, bool can_sleep, +int gpiod_set_array_value_complex(bool raw, bool can_sleep, Same here. Gr{oetje,eeting}s, Geert
Re: [PATCHv5] gpio: Remove VLA from gpiolib
Hi Laura, Thanks for your patch! On Fri, Apr 13, 2018 at 11:24 PM, Laura Abbott wrote: > The new challenge is to remove VLAs from the kernel > (see https://lkml.org/lkml/2018/3/7/621) to eventually > turn on -Wvla. > > Using a kmalloc array is the easy way to fix this but kmalloc is still > more expensive than stack allocation. Introduce a fast path with a > fixed size stack array to cover most chip with gpios below some fixed > amount. The slow path dynamically allocates an array to cover those > chips with a large number of gpios. Blindly replacing VLAs by allocated arrays is IMHO not such a good solution. On the largest systems, NR_GPIOS is 2048, so that makes 2 arrays of 256 bytes. That's an uppper limit, and assumes they are all on the same gpiochip, which they probably aren't. Still, 2 x 256 bytes is a lot, so I agree it should be fixed. So, wouldn't it make more sense to not allocate memory, but just process the request in chunks (say, at most 128 gpios per chunk, i.e. 2 x 16 bytes)? The code already caters for handling chunks due to not all gpios belonging to the same gpiochip. That will probably also be faster than allocating memory, which is the main idea behind this API. > Reviewed-and-tested-by: Lukas Wunner > Signed-off-by: Lukas Wunner > Signed-off-by: Laura Abbott > --- a/drivers/gpio/gpiolib.c > +++ b/drivers/gpio/gpiolib.c > @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, > void *data, > goto err_free_descs; > } > > + if (chip->ngpio > FASTPATH_NGPIO) > + chip_warn(chip, "line cnt %d is greater than fast path cnt > %d\n", > + chip->ngpio, FASTPATH_NGPIO); FWIW, can this warning be triggered from userspace? > @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool > can_sleep, > > while (i < array_size) { > struct gpio_chip *chip = desc_array[i]->gdev->chip; > - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; > - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; Hence just use a fixed size here... > + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; > + unsigned long *mask, *bits; > int first, j, ret; > > + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { > + memset(fastpath, 0, sizeof(fastpath)); > + mask = fastpath; > + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); > + } else { > + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), > + sizeof(*mask), > + can_sleep ? GFP_KERNEL : > GFP_ATOMIC); > + if (!mask) > + return -ENOMEM; > + bits = mask + BITS_TO_LONGS(chip->ngpio); > + } > + > if (!can_sleep) > WARN_ON(chip->can_sleep); > > /* collect all inputs belonging to the same chip */ > first = i; > - memset(mask, 0, sizeof(mask)); > do { > const struct gpio_desc *desc = desc_array[i]; > int hwgpio = gpio_chip_hwgpio(desc); Out-of-context, the code does: | __set_bit(hwgpio, mask); | i++; | } while ((i < array_size) && ... and change this limit to "(i < min(array_size, first + ARRAY_SIZE(mask) * BITS_PER_BYTE))" | (desc_array[i]->gdev->chip == chip)); ... and you're done? > @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip > *chip, > } > } > > -void gpiod_set_array_value_complex(bool raw, bool can_sleep, > +int gpiod_set_array_value_complex(bool raw, bool can_sleep, Same here. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
Re: [PATCHv5] gpio: Remove VLA from gpiolib
On 16/04/2018 13:19, Phil Reid wrote: G'day Laura, One more comment. On 16/04/2018 12:41, Phil Reid wrote: G'day Laura, On 14/04/2018 05:24, Laura Abbott wrote: The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- v5: Dropped some outdated comments and extra whitespace. Switched to ARCH_NR_GPIOS per suggestion of Linus Walleij. --- drivers/gpio/gpiolib.c | 76 +-- drivers/gpio/gpiolib.h | 2 +- include/linux/gpio/consumer.h | 10 +++--- 3 files changed, 66 insertions(+), 22 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index d66de67ef307..79ec7a29b684 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = { .name = "gpio", }; +/* + * Number of GPIOs to use for the fast path in set array + */ +#define FASTPATH_NGPIO ARCH_NR_GPIOS Also wouldn't this mean that fast path will never be triggered now... Just to be clearer. That this will always be true. (chip->ngpio <= FASTPATH_NGPIO) + /* gpio_lock prevents conflicts during gpio_desc[] table updates. * While any GPIO is requested, its gpio_chip is not removable; * each GPIO's "requested" flag serves as a lock and refcount. @@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd, vals[i] = !!ghd.values[i]; /* Reuse the array setting function */ - gpiod_set_array_value_complex(false, + return gpiod_set_array_value_complex(false, true, lh->numdescs, lh->descs, vals); - return 0; } return -EINVAL; } @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); + gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL); if (!gdev->label) { status = -ENOMEM; @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); Previously it looks like just mask was zeroed. So could this just be: memset(mask, 0, BITS_TO_LONGS(chip->ngpio)); I'm guessing it's not a huge additional overhead as it is, but it's more in line with what was there. + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); @@ -2682,8 +2702,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, (desc_array[i]->gdev->chip == chip)); ret = gpio_chip_get_multiple(chip, mask, bits); - if (ret) + if (ret) { + if (mask != fastpath) + kfree(mask); return ret; + } for (j = first; j < i; j++) { const struct gpio_desc *desc = desc_array[j]; @@ -2695,6 +2718,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, value_array[j] = value; trace_gpio_value(desc_to_gpio(desc), 1, value); } + + if (mask != fastpath) + kfree(mask); } return 0; } @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip *chip, } } -void gpiod_set_array_value_complex(bool raw, bool can_sleep, +int gpio
Re: [PATCHv5] gpio: Remove VLA from gpiolib
G'day Laura, One more comment. On 16/04/2018 12:41, Phil Reid wrote: G'day Laura, On 14/04/2018 05:24, Laura Abbott wrote: The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- v5: Dropped some outdated comments and extra whitespace. Switched to ARCH_NR_GPIOS per suggestion of Linus Walleij. --- drivers/gpio/gpiolib.c | 76 +-- drivers/gpio/gpiolib.h | 2 +- include/linux/gpio/consumer.h | 10 +++--- 3 files changed, 66 insertions(+), 22 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index d66de67ef307..79ec7a29b684 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = { .name = "gpio", }; +/* + * Number of GPIOs to use for the fast path in set array + */ +#define FASTPATH_NGPIO ARCH_NR_GPIOS Also wouldn't this mean that fast path will never be triggered now... + /* gpio_lock prevents conflicts during gpio_desc[] table updates. * While any GPIO is requested, its gpio_chip is not removable; * each GPIO's "requested" flag serves as a lock and refcount. @@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd, vals[i] = !!ghd.values[i]; /* Reuse the array setting function */ - gpiod_set_array_value_complex(false, + return gpiod_set_array_value_complex(false, true, lh->numdescs, lh->descs, vals); - return 0; } return -EINVAL; } @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); + gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL); if (!gdev->label) { status = -ENOMEM; @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); Previously it looks like just mask was zeroed. So could this just be: memset(mask, 0, BITS_TO_LONGS(chip->ngpio)); I'm guessing it's not a huge additional overhead as it is, but it's more in line with what was there. + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); @@ -2682,8 +2702,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, (desc_array[i]->gdev->chip == chip)); ret = gpio_chip_get_multiple(chip, mask, bits); - if (ret) + if (ret) { + if (mask != fastpath) + kfree(mask); return ret; + } for (j = first; j < i; j++) { const struct gpio_desc *desc = desc_array[j]; @@ -2695,6 +2718,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, value_array[j] = value; trace_gpio_value(desc_to_gpio(desc), 1, value); } + + if (mask != fastpath) + kfree(mask); } return 0; } @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip *chip, } } -void gpiod_set_array_value_complex(bool raw, bool can_sleep, +int gpiod_set_array_value_complex(bool raw, bool can_sleep, unsigned int array_size, struct
Re: [PATCHv5] gpio: Remove VLA from gpiolib
G'day Laura, On 14/04/2018 05:24, Laura Abbott wrote: The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- v5: Dropped some outdated comments and extra whitespace. Switched to ARCH_NR_GPIOS per suggestion of Linus Walleij. --- drivers/gpio/gpiolib.c| 76 +-- drivers/gpio/gpiolib.h| 2 +- include/linux/gpio/consumer.h | 10 +++--- 3 files changed, 66 insertions(+), 22 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index d66de67ef307..79ec7a29b684 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = { .name = "gpio", }; +/* + * Number of GPIOs to use for the fast path in set array + */ +#define FASTPATH_NGPIO ARCH_NR_GPIOS + /* gpio_lock prevents conflicts during gpio_desc[] table updates. * While any GPIO is requested, its gpio_chip is not removable; * each GPIO's "requested" flag serves as a lock and refcount. @@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd, vals[i] = !!ghd.values[i]; /* Reuse the array setting function */ - gpiod_set_array_value_complex(false, + return gpiod_set_array_value_complex(false, true, lh->numdescs, lh->descs, vals); - return 0; } return -EINVAL; } @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); + gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL); if (!gdev->label) { status = -ENOMEM; @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); Previously it looks like just mask was zeroed. So could this just be: memset(mask, 0, BITS_TO_LONGS(chip->ngpio)); I'm guessing it's not a huge additional overhead as it is, but it's more in line with what was there. + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); @@ -2682,8 +2702,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, (desc_array[i]->gdev->chip == chip)); ret = gpio_chip_get_multiple(chip, mask, bits); - if (ret) + if (ret) { + if (mask != fastpath) + kfree(mask); return ret; + } for (j = first; j < i; j++) { const struct gpio_desc *desc = desc_array[j]; @@ -2695,6 +2718,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, value_array[j] = value; trace_gpio_value(desc_to_gpio(desc), 1, value); } + + if (mask != fastpath) +
[PATCHv5] gpio: Remove VLA from gpiolib
The new challenge is to remove VLAs from the kernel (see https://lkml.org/lkml/2018/3/7/621) to eventually turn on -Wvla. Using a kmalloc array is the easy way to fix this but kmalloc is still more expensive than stack allocation. Introduce a fast path with a fixed size stack array to cover most chip with gpios below some fixed amount. The slow path dynamically allocates an array to cover those chips with a large number of gpios. Reviewed-and-tested-by: Lukas Wunner Signed-off-by: Lukas Wunner Signed-off-by: Laura Abbott --- v5: Dropped some outdated comments and extra whitespace. Switched to ARCH_NR_GPIOS per suggestion of Linus Walleij. --- drivers/gpio/gpiolib.c| 76 +-- drivers/gpio/gpiolib.h| 2 +- include/linux/gpio/consumer.h | 10 +++--- 3 files changed, 66 insertions(+), 22 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index d66de67ef307..79ec7a29b684 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -61,6 +61,11 @@ static struct bus_type gpio_bus_type = { .name = "gpio", }; +/* + * Number of GPIOs to use for the fast path in set array + */ +#define FASTPATH_NGPIO ARCH_NR_GPIOS + /* gpio_lock prevents conflicts during gpio_desc[] table updates. * While any GPIO is requested, its gpio_chip is not removable; * each GPIO's "requested" flag serves as a lock and refcount. @@ -399,12 +404,11 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd, vals[i] = !!ghd.values[i]; /* Reuse the array setting function */ - gpiod_set_array_value_complex(false, + return gpiod_set_array_value_complex(false, true, lh->numdescs, lh->descs, vals); - return 0; } return -EINVAL; } @@ -1192,6 +1196,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data, goto err_free_descs; } + if (chip->ngpio > FASTPATH_NGPIO) + chip_warn(chip, "line cnt %d is greater than fast path cnt %d\n", + chip->ngpio, FASTPATH_NGPIO); + gdev->label = kstrdup_const(chip->label ?: "unknown", GFP_KERNEL); if (!gdev->label) { status = -ENOMEM; @@ -2662,16 +2670,28 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, while (i < array_size) { struct gpio_chip *chip = desc_array[i]->gdev->chip; - unsigned long mask[BITS_TO_LONGS(chip->ngpio)]; - unsigned long bits[BITS_TO_LONGS(chip->ngpio)]; + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)]; + unsigned long *mask, *bits; int first, j, ret; + if (likely(chip->ngpio <= FASTPATH_NGPIO)) { + memset(fastpath, 0, sizeof(fastpath)); + mask = fastpath; + bits = fastpath + BITS_TO_LONGS(FASTPATH_NGPIO); + } else { + mask = kcalloc(2 * BITS_TO_LONGS(chip->ngpio), + sizeof(*mask), + can_sleep ? GFP_KERNEL : GFP_ATOMIC); + if (!mask) + return -ENOMEM; + bits = mask + BITS_TO_LONGS(chip->ngpio); + } + if (!can_sleep) WARN_ON(chip->can_sleep); /* collect all inputs belonging to the same chip */ first = i; - memset(mask, 0, sizeof(mask)); do { const struct gpio_desc *desc = desc_array[i]; int hwgpio = gpio_chip_hwgpio(desc); @@ -2682,8 +2702,11 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, (desc_array[i]->gdev->chip == chip)); ret = gpio_chip_get_multiple(chip, mask, bits); - if (ret) + if (ret) { + if (mask != fastpath) + kfree(mask); return ret; + } for (j = first; j < i; j++) { const struct gpio_desc *desc = desc_array[j]; @@ -2695,6 +2718,9 @@ int gpiod_get_array_value_complex(bool raw, bool can_sleep, value_array[j] = value; trace_gpio_value(desc_to_gpio(desc), 1, value); } + + if (mask != fastpath) + kfree(mask); } return 0; } @@ -2878,7 +2904,7 @@ static void gpio_chip_set_multiple(struct gpio_chip *chip, } } -void gpiod_set_array_value_complex(bool raw, bool can_sleep, +int gpiod_set_array_v