linux-kernel - Re: [PATCH AUTOSEL 5.4 128/350] spi: pxa2xx: Set controller->max_transfer

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Message-ID: <20191219173504.GN17708@sasha-vm>
Date:   Thu, 19 Dec 2019 12:35:04 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.4 128/350] spi: pxa2xx: Set
 controller->max_transfer_size in dma mode

On Wed, Dec 11, 2019 at 10:47:38AM +0000, Mark Brown wrote:
>On Tue, Dec 10, 2019 at 04:03:53PM -0500, Sasha Levin wrote:
>> From: Daniel Vetter <daniel.vetter@...ll.ch>
>>
>> [ Upstream commit b2662a164f9dc48da8822e56600686d639056282 ]
>>
>> In DMA mode we have a maximum transfer size, past that the driver
>> falls back to PIO (see the check at the top of pxa2xx_spi_transfer_one).
>> Falling back to PIO for big transfers defeats the point of a dma engine,
>> hence set the max transfer size to inform spi clients that they need
>> to do something smarter.
>
>This won't fix anything by itself, this asks other code to change how it
>behaves which may or may not work in older kernels.

I'll drop it then, thanks!

-- 
Thanks,
Sasha