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

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Message-ID: <20191211104738.GA3870@sirena.org.uk>
Date:   Wed, 11 Dec 2019 10:47:38 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Sasha Levin <sashal@...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 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.

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