On Tue, Sep 24, 2019 at 10:47:28AM -0700, Nick Desaulniers wrote:
> Fixes the following 2 issues in the driver:
> 1. Left shifting a signed integer is undefined behavior. Unsigned
>    integral types should be used for bitwise operations.
> 2. The delay scales from 0x0010 to 0x20000 by powers of 2, but udelay
>    will result in a linkage failure when given a constant that's greater
>    than 20000 (0x4E20). Agressive loop unrolling can fully unroll the
>    loop, resulting in later iterations overflowing the call to udelay.
> 
> 2 is fixed via splitting the loop in two, iterating the first up to the
> point where udelay would overflow, then switching to mdelay, as
> suggested in Documentation/timers/timers-howto.rst.
> 
> Reported-by: Tomasz PaweĊ‚ Gajc <tpg...@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/678
> Debugged-by: Nathan Chancellor <natechancel...@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulni...@google.com>
> ---
> Changes V1 -> V2:
> * The first loop in send_byte() needs to break out on the same condition
>   now. Technically, the loop condition could even be removed. The diff
>   looks funny because of the duplicated logic between existing and newly
>   added for loops.
> 
>  drivers/hwmon/applesmc.c | 35 +++++++++++++++++++++++++++++++----
>  1 file changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index 183ff3d25129..c76adb504dff 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -46,6 +46,7 @@
>  #define APPLESMC_MIN_WAIT    0x0010
>  #define APPLESMC_RETRY_WAIT  0x0100
>  #define APPLESMC_MAX_WAIT    0x20000
> +#define APPLESMC_UDELAY_MAX  20000
>  
>  #define APPLESMC_READ_CMD    0x10
>  #define APPLESMC_WRITE_CMD   0x11
> @@ -157,14 +158,23 @@ static struct workqueue_struct *applesmc_led_wq;
>  static int wait_read(void)
>  {
>       u8 status;
> -     int us;
> -     for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> +     unsigned int us;
> +
> +     for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) {
>               udelay(us);
>               status = inb(APPLESMC_CMD_PORT);
>               /* read: wait for smc to settle */
>               if (status & 0x01)
>                       return 0;
>       }
> +     /* switch to mdelay for longer sleeps */
> +     for (; us < APPLESMC_MAX_WAIT; us <<= 1) {
> +             mdelay(us);
> +             status = inb(APPLESMC_CMD_PORT);
> +             /* read: wait for smc to settle */
> +             if (status & 0x01)
> +                     return 0;
> +     }
>  
>       pr_warn("wait_read() fail: 0x%02x\n", status);
>       return -EIO;
> @@ -177,10 +187,10 @@ static int wait_read(void)
>  static int send_byte(u8 cmd, u16 port)
>  {
>       u8 status;
> -     int us;
> +     unsigned int us;
>  
>       outb(cmd, port);
> -     for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> +     for (us = APPLESMC_MIN_WAIT; us < APPLESMC_UDELAY_MAX; us <<= 1) {
>               udelay(us);
>               status = inb(APPLESMC_CMD_PORT);
>               /* write: wait for smc to settle */
> @@ -190,6 +200,23 @@ static int send_byte(u8 cmd, u16 port)
>               if (status & 0x04)
>                       return 0;
>               /* timeout: give up */
> +             if (us << 1 == APPLESMC_UDELAY_MAX)
> +                     break;
> +             /* busy: long wait and resend */
> +             udelay(APPLESMC_RETRY_WAIT);
> +             outb(cmd, port);
> +     }
> +     /* switch to mdelay for longer sleeps */
> +     for (; us < APPLESMC_MAX_WAIT; us <<= 1) {
> +             mdelay(us);
> +             status = inb(APPLESMC_CMD_PORT);
> +             /* write: wait for smc to settle */
> +             if (status & 0x02)
> +                     continue;
> +             /* ready: cmd accepted, return */
> +             if (status & 0x04)
> +                     return 0;
> +             /* timeout: give up */
>               if (us << 1 == APPLESMC_MAX_WAIT)
>                       break;
>               /* busy: long wait and resend */
> -- 
> 2.23.0.351.gc4317032e6-goog
> 

This resolves the __bad_udelay appearance at -O3 for me. I am not
familiar enough with this code to give a reviewed by though!

Also, for some odd reason, I couldn't apply your patch with 'git apply':

% curl -LSs 
https://lore.kernel.org/lkml/20190924174728.201464-1-ndesaulni...@google.com/raw
 | git apply
error: corrupt patch at line 117

It looks like some of the '=' got changed into =3D and some spaces got
changed into =20. Weird encoding glitch?

Cheers,
Nathan

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