Re: [PATCH] drivers: spi: core: Add optional stall delay between cs_change transfers

[Geert Uytterhoeven]

Hi Stefan,

Thanks for your patch!

On Tue, Feb 19, 2019 at 6:02 PM Stefan Popa  wrote:
> From: Michael Hennerich 
>
> Some devices like the ADIS16460 IMU require a stall period between
> transfers.

This is not just about the period between transfers (which is handled by
delay_usecs), but about the period in between chipselect pulses if
cs_change is set.

> The default value of 10us are not enough. Introduce a per

... is not enough.

> transfer configurable delay.

> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1144,7 +1144,8 @@ static int spi_transfer_one_message(struct 
> spi_controller *ctlr,
> keep_cs = true;
> } else {
> spi_set_cs(msg->spi, false);
> -   udelay(10);
> +   udelay(xfer->cs_change_stall_delay_us ?
> +  xfer->cs_change_stall_delay_us : 10);
> spi_set_cs(msg->spi, true);
> }
> }
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 314d922..273774c 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -702,6 +702,8 @@ extern void spi_res_release(struct spi_controller *ctlr,
>   *  transfer. If 0 the default (from @spi_device) is used.
>   * @bits_per_word: select a bits_per_word other than the device default
>   *  for this transfer. If 0 the default (from @spi_device) is used.
> + * @cs_change_stall_delay_us: microseconds to delay between cs_change
> + * transfers.

I think this needs some better wording, too.
Else it is hard to understand how this is different from delay_usecs,
without looking at the implementation.

>   * @cs_change: affects chipselect after this transfer completes
>   * @delay_usecs: microseconds to delay after this transfer before
>   * (optionally) changing the chipselect status, then starting
> @@ -788,6 +790,7 @@ struct spi_transfer {
>  #defineSPI_NBITS_DUAL  0x02 /* 2bits transfer */
>  #defineSPI_NBITS_QUAD  0x04 /* 4bits transfer */
> u8  bits_per_word;
> +   u8  cs_change_stall_delay_us;
> u16 delay_usecs;
> u32 speed_hz;
> u16 word_delay;

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

[PATCH] drivers: spi: core: Add optional stall delay between cs_change transfers

[Stefan Popa]

From: Michael Hennerich 

Some devices like the ADIS16460 IMU require a stall period between
transfers. The default value of 10us are not enough. Introduce a per
transfer configurable delay.

Signed-off-by: Michael Hennerich 
Signed-off-by: Stefan Popa 
---
 drivers/spi/spi.c   | 3 ++-
 include/linux/spi/spi.h | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9a7def7..717b92a 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1144,7 +1144,8 @@ static int spi_transfer_one_message(struct spi_controller 
*ctlr,
keep_cs = true;
} else {
spi_set_cs(msg->spi, false);
-   udelay(10);
+   udelay(xfer->cs_change_stall_delay_us ?
+  xfer->cs_change_stall_delay_us : 10);
spi_set_cs(msg->spi, true);
}
}
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 314d922..273774c 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -702,6 +702,8 @@ extern void spi_res_release(struct spi_controller *ctlr,
  *  transfer. If 0 the default (from @spi_device) is used.
  * @bits_per_word: select a bits_per_word other than the device default
  *  for this transfer. If 0 the default (from @spi_device) is used.
+ * @cs_change_stall_delay_us: microseconds to delay between cs_change
+ * transfers.
  * @cs_change: affects chipselect after this transfer completes
  * @delay_usecs: microseconds to delay after this transfer before
  * (optionally) changing the chipselect status, then starting
@@ -788,6 +790,7 @@ struct spi_transfer {
 #defineSPI_NBITS_DUAL  0x02 /* 2bits transfer */
 #defineSPI_NBITS_QUAD  0x04 /* 4bits transfer */
u8  bits_per_word;
+   u8  cs_change_stall_delay_us;
u16 delay_usecs;
u32 speed_hz;
u16 word_delay;
-- 
2.7.4