linux-kernel - Re: [PATCH] mmc: tmio: simplify the DMA mode test

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Date:   Mon, 15 Oct 2018 00:36:36 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mmc@...r.kernel.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] mmc: tmio: simplify the DMA mode test

On Sat, Oct 13, 2018 at 12:03:08AM +0900, Masahiro Yamada wrote:
> host->chan_{rx,tx} represents the DMA capability of the platform.
> Even if DMA is supported, there are cases where we want to use PIO,
> for example, data length is short enough as commit 5f52c3552946
> ("mmc: tmio: use PIO for short transfers") mentioned.
> 
> Regarding the hardware control flow, we are interested in whether DMA
> is currently enabled or not, instead of whether the platform has the
> DMA capability.
> 
> Hence, the several conditionals in tmio_mmc_core.c end up with
> checking host->chan_{rx,tx} and !host->force_pio. This is not nice.
> 
> Let's flip the flag host->force_pio into host->dma_on.
> 
> host->dma_on represents whether the DMA is currently enabled or not.
> This flag is set false in the beginning of each command, then should
> be set true by tmio_mmc_start_dma() when the DMA is turned on.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

I like it. Much easier to read!

Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Also here, I'd like to test this on Monday on some more devices.


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