linux-kernel - Re: [PATCH V2 1/2] mfd: cros ec: spi: Don't send first message too soon

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Date:   Wed, 29 Nov 2017 11:15:50 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Shawn Nematbakhsh <shawnn@...omium.org>,
        Benson Leung <bleung@...omium.org>, stable@...r.kernel.org
Subject: Re: [PATCH V2 1/2] mfd: cros ec: spi: Don't send first message too
 soon

On Tue, 28 Nov 2017, Jon Hunter wrote:
> On 14/11/17 14:43, 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.
> > 
> > Cc: <stable@...r.kernel.org>
> > 
> > Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> > Reviewed-by: Brian Norris <briannorris@...omium.org>
> > ---
> > Changes since V1:
> > - Added stable-tag and Brian's reviewed-by.
> > 
> > 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.
> > 
> >  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();
> >  
> >  	err = cros_ec_register(ec_dev);
> >  	if (err) {
> 
> Can you queue this as a fix for v4.15-rc1?

No, but I will submit it for one of the v4.15-rcs.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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