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From: Enric Balletbo i Serra <enric.balletbo@collabora.com>
To: Douglas Anderson <dianders@chromium.org>,
	Mark Brown <broonie@kernel.org>,
	Benson Leung <bleung@chromium.org>
Cc: linux-rockchip@lists.infradead.org, drinkcat@chromium.org,
	Guenter Roeck <groeck@chromium.org>,
	briannorris@chromium.org, mka@chromium.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 3/3] platform/chrome: cros_ec_spi: Request the SPI thread be realtime
Date: Tue, 21 May 2019 09:50:54 +0200	[thread overview]
Message-ID: <74a31886-fa49-cabf-aa11-25b402e80414@collabora.com> (raw)
In-Reply-To: <20190515164814.258898-4-dianders@chromium.org>

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;
> 

  reply	other threads:[~2019-05-21  7:51 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-15 16:48 [PATCH v4 0/3] spi: A better solution for cros_ec_spi reliability Douglas Anderson
2019-05-15 16:48 ` [PATCH v4 1/3] platform/chrome: cros_ec_spi: Move to real time priority for transfers Douglas Anderson
2019-05-15 17:02   ` Guenter Roeck
2019-05-21  7:52     ` Enric Balletbo i Serra
2019-05-15 16:48 ` [PATCH v4 2/3] spi: Allow SPI devices to request the pumping thread be realtime Douglas Anderson
2019-05-21  7:49   ` Enric Balletbo i Serra
2019-05-23 13:46   ` Mark Brown
2019-05-23 13:49   ` Applied "spi: Allow SPI devices to request the pumping thread be realtime" to the spi tree Mark Brown
2019-05-15 16:48 ` [PATCH v4 3/3] platform/chrome: cros_ec_spi: Request the SPI thread be realtime Douglas Anderson
2019-05-21  7:50   ` Enric Balletbo i Serra [this message]
2019-05-24 10:26   ` Enric Balletbo i Serra

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