+ others
On Mon, Nov 13, 2017 at 09:05:39PM +0000, Jon Hunter wrote:
> On the Tegra124 Nyan-Big chromebook the very first SPI message sent to
> the EC is failing.
>
> The Tegra SPI driver configures the SPI chip-selects to be active-high
> by default (and always has for many years). The EC SPI requires an
> active-low chip-select and so the Tegra chip-select is reconfigured to
> be active-low when the EC SPI driver calls spi_setup(). The problem is
> that if the first SPI message to the EC is sent too soon after
> reconfiguring the SPI chip-select, it fails.
>
> The EC SPI driver prevents back-to-back SPI messages being sent too
> soon by keeping track of the time the last transfer was sent via the
> variable 'last_transfer_ns'. To prevent the very first transfer being
> sent too soon, initialise the 'last_transfer_ns' variable after calling
> spi_setup() and before sending the first SPI message.
>
> Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
> ---
> Looks like this issue has been around for several Linux releases now
> and it just depends on timing if this issue is seen or not and so there
> is no specific commit this fixes. However, would be good to include for
> v4.15.
I wonder if that doesn't mean we should have a stable tag still?
Cc: <stable@xxxxxxxxxxxxxxx>
> drivers/mfd/cros_ec_spi.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/mfd/cros_ec_spi.c b/drivers/mfd/cros_ec_spi.c
> index c9714072e224..a14196e95e9b 100644
> --- a/drivers/mfd/cros_ec_spi.c
> +++ b/drivers/mfd/cros_ec_spi.c
> @@ -667,6 +667,7 @@ static int cros_ec_spi_probe(struct spi_device *spi)
> sizeof(struct ec_response_get_protocol_info);
> ec_dev->dout_size = sizeof(struct ec_host_request);
>
> + ec_spi->last_transfer_ns = ktime_get_ns();
Seems pretty reasonable to me:
Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxxx>
>
> err = cros_ec_register(ec_dev);
> if (err) {
> --
> 2.7.4
>
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