linux-kernel - Re: [PATCH v4 0/6] spi: spi-fsl-dspi: Target mode improvements

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Message-ID: <578e01d9-20bc-48f1-aada-579276f6a9d1@sirena.org.uk>
Date: Tue, 1 Jul 2025 16:30:54 +0100
From: Mark Brown <broonie@...nel.org>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: James Clark <james.clark@...aro.org>,
	Vladimir Oltean <olteanv@...il.com>, Arnd Bergmann <arnd@...db.de>,
	Larisa Grigore <larisa.grigore@....com>,
	Frank Li <Frank.li@....com>, Christoph Hellwig <hch@....de>,
	linux-spi@...r.kernel.org, imx@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/6] spi: spi-fsl-dspi: Target mode improvements

On Tue, Jul 01, 2025 at 06:24:33PM +0300, Vladimir Oltean wrote:
> On Tue, Jul 01, 2025 at 04:16:50PM +0100, Mark Brown wrote:

> > Switching between modes is incredibly common, usually between PIO (for
> > very short transfers) and DMA, that's no problem.  Factoring in
> > timestamping seems like a reasonable signal I guess, might trip someone
> > who was trying to benchmark things up but probably not normal users.

> Ah, ok, I vaguely remember something being discussed about can_dma()
> on previous iterations of this patch, but in a different context.
> Then that's an avenue to explore, I guess. Looking at that method's
> prototype, I suppose dspi could simply return can_dma = false "if (xfer->ptp_sts)"
> (timestamp requested), i.e. no core involvement in the decision process at all?

Yes, exactly.  It can base the decision on whatever amuses it about the
transfer.

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