linux-kernel - Re: [PATCH v5 3/7] spi: spi-fsl-dspi: Stub out DMA functions

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Message-ID: <ce55ed06-7326-473b-a2f9-40b0bc61c396@linaro.org>
Date: Mon, 1 Sep 2025 10:09:10 +0100
From: James Clark <james.clark@...aro.org>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: Vladimir Oltean <olteanv@...il.com>, Mark Brown <broonie@...nel.org>,
 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 v5 3/7] spi: spi-fsl-dspi: Stub out DMA functions



On 29/08/2025 3:26 pm, Vladimir Oltean wrote:
> Hi James,
> 
> On Fri, Aug 29, 2025 at 12:46:45PM +0100, James Clark wrote:
>> This will allow the build to succeed with !CONFIG_DMA_ENGINE, either due
>> to a randconfig build test or when the target only uses one of the
>> non-DMA transfer modes which this driver supports.
>>
>> Signed-off-by: James Clark <james.clark@...aro.org>
>> ---
> 
> Sorry for not paying attention to this previously. I didn't pick up from
> previous conversations what problem this is addressing. I built an arm64
> kernel with CONFIG_DMA_ENGINE disabled (by unsetting CONFIG_DMADEVICES)
> and it got built successfully. The .config is attached.

Did you test with or without these patches applied? It's only needed to 
make the commit "spi: spi-fsl-dspi: Use non-coherent memory for DMA" 
build because that's a newer function that isn't stubbed out like the 
old ones.

I originally tried to fix it in the DMA code so it got spun out into a 
new thread, which is probably why you missed it. And the commit message 
is missing the reported-by and closes tags which I'll add.

> 
> Please post the specific build error if you haven't done so already, and
> give a reasonable hint at the technical motivation in the commit message.

The reason we saw the issue was a randconfig build. But it's possible 
that someone is building the driver without DMA as well, hence: "or when 
the target only uses one of the non-DMA transfer modes which this driver 
supports".

The new commit message can be:

   spi: spi-fsl-dspi: Stub out DMA functions

   In a later commit we'll use dma_alloc_noncoherent() which isn't
   stubbed out for builds without CONFIG_DMA_ENGINE and results in the
   following build error:

     spi-fsl-dspi.c:(.text+0x644): undefined reference to
        `dma_free_pages'
     m68k-linux-ld: spi-fsl-dspi.c:(.text+0x67a): undefined reference to
        `dma_free_pages'

   To continue to support devices that only need XSPI mode and so that
   randconfig builds work, stub out DMA functionality in the DSPI driver.

   Reported-by: kernel test robot <lkp@...el.com>
   Closes: 
https://lore.kernel.org/oe-kbuild-all/202506160036.t9VDxF6p-lkp@intel.com/
   Signed-off-by: James Clark <james.clark@...aro.org>