linux-kernel - Re: [PATCH] i2c: davinci: fix the cpufreq transition

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Date:   Tue, 23 Jan 2018 18:08:57 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <brgl@...ev.pl>,
        Kevin Hilman <khilman@...nel.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        David Lechner <david@...hnology.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH] i2c: davinci: fix the cpufreq transition

On Monday 22 January 2018 08:12 PM, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> i2c_davinci_cpufreq_transition() is implemented in a way that will
> block if it ever gets called while no transfer is in progress.

true!

> 
> Not only that, but reinit_completion() is never called for xfr_complete.

reinit_completion() use is must only with complete_all(). At least that
bug is not obvious so needs more detail to be added here.

> Use the fact that cpufreq uses an srcu_notifier (running in process
> context) for transitions and that the bus_lock is taken during the call
> to master_xfer() and simplify the code by removing the transfer
> completion entirely and protecting i2c_davinci_cpufreq_transition()
> with i2c_lock/unlock_adapter().
> 
> Reported-by: David Lechner <david@...hnology.com>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>

I assume you tested this on a board where I2C-controlled PMIC changes
voltage during CPUfreq (DA850 LogicPD EVM should have this hardware
support).

Perhaps also add:

Fixes: 82c0de11b734 ("i2c: davinci: Add cpufreq support")

Apart from that:

Reviewed-by: Sekhar Nori <nsekhar@...com>

Thanks,
Sekhar