linux-kernel - Re: [PATCH v3 3/6] spi: spi-fsl-dspi: Stub out DMA functions

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Message-Id: <0f904f12-295c-48fe-96c7-c64c461cdbbd@app.fastmail.com>
Date: Wed, 25 Jun 2025 12:00:38 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "James Clark" <james.clark@...aro.org>, "Frank Li" <Frank.li@....com>
Cc: "Vladimir Oltean" <olteanv@...il.com>, "Mark Brown" <broonie@...nel.org>,
 "Vladimir Oltean" <vladimir.oltean@....com>,
 "Larisa Grigore" <larisa.grigore@....com>, "Christoph Hellwig" <hch@....de>,
 linux-spi@...r.kernel.org, imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/6] spi: spi-fsl-dspi: Stub out DMA functions

On Wed, Jun 25, 2025, at 11:19, James Clark wrote:
> On 24/06/2025 6:16 pm, Arnd Bergmann wrote:
>> On Tue, Jun 24, 2025, at 18:29, Frank Li wrote:
>
>> It would also be simpler to enforce this in Kconfig if we only
>> care about users that use the DMA support.
>
> But most of the devices supported by the driver don't do any DMA. That 
> was the reason to stub them out rather than add the Kconfig depends.

Ah right. So even when running on SoCs that have a DMA engine,
you can end up not using it?

In this case you could have an extra Kconfig symbol to configure
DMA support for this driver and use that in the source code:

config SPI_FSL_DSPI_DMA
      bool "Use DMA engine for offloading Freescale DSPI transfers"
      depends on SPI_FSL_DSPI && DMA_ENGINE
      help
         ....


     Arnd