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

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Message-ID: <20171129110725.cszh6o6s5n7cyn4s@dell>
Date:   Wed, 29 Nov 2017 11:07:25 +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>
Subject: Re: [PATCH 1/2] mfd: cros ec: spi: Don't send first message too soon

On Mon, 13 Nov 2017, 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@...dia.com>
> ---
> 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(+)

Applied, thanks.

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