linux-kernel - Re: [PATCH v1] i2c: tegra: Remove suspend-resume

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Message-ID: <20180514115933.GH18312@ulmo>
Date:   Mon, 14 May 2018 13:59:33 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Shardar Shariff Md <smohammed@...dia.com>,
        linux-tegra@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] i2c: tegra: Remove suspend-resume

On Mon, May 14, 2018 at 12:13:47AM +0300, Dmitry Osipenko wrote:
> Nothing prevents I2C clients to access I2C while Tegra's driver is being
> suspended, this results in -EBUSY error returned to the clients and that
> may have unfortunate consequences. In particular this causes problems
> for the TPS6586x MFD driver which emits hundreds of "failed to read
> interrupt status" error messages on resume from suspend. This happens if
> TPS6586X is used to wake system from suspend by the expired RTC alarm
> timer because TPS6586X is an I2C device driver and its IRQ handler reads
> the status register while Tegra's I2C driver is suspended, i.e. just after
> kernel enabled IRQ's during of resume-from-suspend process.
> 
> Note that the removed tegra_i2c_resume() invoked tegra_i2c_init() which
> performs HW reset. That seems was also not entirely correct because moving
> tegra_i2c_resume to an earlier stage of resume-from-suspend process causes
> I2C transfer to fail in the case of TPS6586X. It is fine to remove the
> HW-reinitialization for now because it should be only needed in a case of
> using lowest power-mode during suspend, which upstream kernel doesn't
> support.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> Cc: <stable@...r.kernel.org>
> ---
>  drivers/i2c/busses/i2c-tegra.c | 33 ---------------------------------
>  1 file changed, 33 deletions(-)

Shardar, Laxman, any thoughts on this? The is_suspended thing looks to
me like a workaround of some sort that may not be needed if clients have
proper suspend/resume implementations. Even without suspend/resume
support in client drivers, the driver core should resume devices in the
right order (I2C adapter before any of the clients), so I don't see any
cases where the is_suspended logic would be useful.

Thierry

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