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SubjectRe: [PATCH v4 3/3] platform/chrome: cros_ec_spi: Request the SPI thread be realtime
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Hi,

On 15/5/19 18:48, Douglas Anderson wrote:
> All currently known ECs in the wild are very sensitive to timing.
> Specifically the ECs are known to drop a transfer if more than 8 ms
> passes from the assertion of the chip select until the transfer
> finishes.
>
> Let's use the new feature introduced in the patch (spi: Allow SPI
> devices to request the pumping thread be realtime") to request the SPI
> pumping thread be realtime. This means that if we get shunted off to
> the SPI thread for whatever reason we won't get downgraded to low
> priority.
>
> NOTES:
> - We still need to keep ourselves as high priority since the SPI core
> doesn't guarantee that all transfers end up on the pumping thread
> (in fact, it tries pretty hard to do them in the calling context).
> - If future Chrome OS ECs ever fix themselves to be less sensitive
> then we could consider adding a property (or compatible string) to
> not set this property. For now we need it across the board.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Guenter Roeck <groeck@chromium.org>

For my own reference:

Acked-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Thanks,
Enric

> ---
>
> Changes in v4: None
> Changes in v3:
> - Updated description and variable name since we no longer force.
>
> Changes in v2:
> - Renamed variable to "force_rt_transfers".
>
> drivers/platform/chrome/cros_ec_spi.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/platform/chrome/cros_ec_spi.c b/drivers/platform/chrome/cros_ec_spi.c
> index 1e38a885c539..daf3119191c8 100644
> --- a/drivers/platform/chrome/cros_ec_spi.c
> +++ b/drivers/platform/chrome/cros_ec_spi.c
> @@ -740,6 +740,7 @@ static int cros_ec_spi_probe(struct spi_device *spi)
>
> spi->bits_per_word = 8;
> spi->mode = SPI_MODE_0;
> + spi->rt = true;
> err = spi_setup(spi);
> if (err < 0)
> return err;
>

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