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

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Date:   Sat, 18 Nov 2017 22:09:58 -0800
From:   Benson Leung <bleung@...gle.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Lee Jones <lee.jones@...aro.org>, 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

Hi Jon,

On Tue, Nov 14, 2017 at 02:43:27PM +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.
> 
> Cc: <stable@...r.kernel.org>
> 
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
> Reviewed-by: Brian Norris <briannorris@...omium.org>

Acked-by: Benson Leung <bleung@...omium.org>

-- 
Benson Leung
Staff Software Engineer
Chrome OS Kernel
Google Inc.
bleung@...gle.com
Chromium OS Project
bleung@...omium.org

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