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

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Message-ID: <20200917114716.GZ3515672@ulmo>
Date:   Thu, 17 Sep 2020 13:47:16 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...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

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.

Thierry

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