linux-kernel - Re: [PATCH v7 21/34] i2c: tegra: Don't fall back to PIO mode if DMA configuration fails

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Date:   Thu, 17 Sep 2020 18:03:04 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 21/34] i2c: tegra: Don't fall back to PIO mode if DMA
 configuration fails

17.09.2020 14:47, Thierry Reding пишет:
> On Wed, Sep 09, 2020 at 01:39:53AM +0300, Dmitry Osipenko wrote:
>> The DMA code path has been tested well enough and the DMA configuration
>> performed by tegra_i2c_config_fifo_trig() shouldn't ever fail in practice.
>> Hence let's remove the obscure transfer-mode switching in order to have a
>> cleaner and simpler code. Now I2C transfer will be failed if DMA
>> configuration fails.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/i2c/busses/i2c-tegra.c | 18 ++++++++++--------
>>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> I'm not sure that's a good idea. It's always possible that the DMA setup
> is going to break because of something that's not related to the I2C
> driver itself. Having the system completely break instead of falling
> back to PIO mode seems like it would only complicate troubleshooting any
> such issues.

That code has zero test coverage because this problem never happens in
practice, hence it should be better to have it removed. We may consider
re-adding it back if there will be a real-world incident, okay?