linux-kernel - Re: [PATCH V5 3/5] i2c: tegra: Add DMA Support

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Date:   Wed, 30 Jan 2019 04:42:14 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <mkarthik@...dia.com>, <smohammed@...dia.com>, <talho@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH V5 3/5] i2c: tegra: Add DMA Support

В Tue, 29 Jan 2019 15:16:09 -0800
Sowjanya Komatineni <skomatineni@...dia.com> пишет:

> This patch adds DMA support for Tegra I2C.
> 
> Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for
> transfer size of the max FIFO depth and DMA mode is used for
> transfer size higher than max FIFO depth to save CPU overhead.
> 
> PIO mode needs full intervention of CPU to fill or empty FIFO's
> and also need to service multiple data requests interrupt for the
> same transaction. This adds delay between data bytes of the same
> transfer when CPU is fully loaded and some slave devices has
> internal timeout for no bus activity and stops transaction to
> avoid bus hang. DMA mode is helpful in such cases.
> 
> DMA mode is also helpful for Large transfers during downloading or
> uploading FW over I2C to some external devices.
> 
> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
> ---
>  [V5] : Same as V4
>  [V4] : Updated to allocate DMA buffer only when DMA mode.
> 	Updated to fall back to PIO mode when DMA channel request or
> 	buffer allocation fails.
>  [V3] : Updated without additional buffer allocation.
>  [V2] : Updated based on V1 review feedback along with code cleanup
> for proper implementation of DMA.

Could you please tell whether you missed my comments to V3 [0] or chose
to ignore them? If the former, then I'd want to get answers to those
questions and comments. I'll stop here for now.

[0] https://patchwork.ozlabs.org/patch/1031379/