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

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Message-ID: <20250612143644.cmw6d4iiootipafp@skbuf>
Date: Thu, 12 Jun 2025 17:36:44 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: James Clark <james.clark@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>, Frank Li <Frank.li@....com>,
	Vladimir Oltean <olteanv@...il.com>,
	Mark Brown <broonie@...nel.org>, 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 03:14:32PM +0100, James Clark wrote:
> > FWIW, the XSPI FIFO performance should be higher.
> 
> This leads me to realise a mistake in my original figures. My head was stuck
> in target mode where we use DMA so I forgot to force DMA in host mode to run
> the performance tests. The previous figures were all XSPI mode and the small
> difference in performance could have been just down to the layout of the
> code changing?
> 
> Changing it to DMA mode gives figures that make much more sense:
> 
> Coherent (4096 byte transfers): 6534 kbps
> Non-coherent:                   7347 kbps
> 
> Coherent (16 byte transfers):    447 kbps
> Non-coherent:                    448 kbps
> 
> 
> Just for comparison running the same test in XSPI mode:
> 
> 4096 byte transfers:            2143 kbps
> 16 byte transfers:               637 kbps

So to be clear, the 'non-coherent' test was done just with patch 2
applied, or also with 3?