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SubjectRe: [PATCH] drivers: spi: core: Add optional stall delay between cs_change transfers
Hi Stefan,

Thanks for your patch!

On Tue, Feb 19, 2019 at 6:02 PM Stefan Popa <stefan.popa@analog.com> wrote:
> From: Michael Hennerich <michael.hennerich@analog.com>
>
> 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 {
> #define SPI_NBITS_DUAL 0x02 /* 2bits transfer */
> #define SPI_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 -- geert@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

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