linux-kernel - Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

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Message-ID: <20250612155143.bn3xw5tf7hfvr5id@skbuf>
Date: Thu, 12 Jun 2025 18:51:43 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: James Clark <james.clark@...aro.org>
Cc: Mark Brown <broonie@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Frank Li <Frank.li@....com>, Vladimir Oltean <olteanv@...il.com>,
	linux-spi@...r.kernel.org, imx@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

On Thu, Jun 12, 2025 at 04:47:26PM +0100, James Clark wrote:
> > This is a fairly normal pattern, it's a big part of why the can_dma()
> > callback is per transfer - so you can do a copybreak and use PIO for
> > smaller transfers where the overhead of setting up DMA is often more
> > than the overhead of just doing PIO.
> 
> Makes sense. Although for some reason two devices already use DMA for host
> mode and it's not that clear to me what the reason is.

I couldn't test them and I've kept them as they were.