Messages in this thread | | | From | Doug Anderson <> | Date | Mon, 17 Apr 2023 07:07:28 -0700 | Subject | Re: [PATCH v3 3/3] spi: spi-qcom-qspi: Add DMA mode support |
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Hi,
On Mon, Apr 17, 2023 at 5:12 AM Mark Brown <broonie@kernel.org> wrote: > > On Fri, Apr 14, 2023 at 03:05:58PM -0700, Doug Anderson wrote: > > > Having alignment requirements like this doesn't seem like it should be > > that unusual, though, and that's why it feels like the logic belongs > > in the SPI core. In fact, it seems like this is _supposed_ to be > > handled in the SPI core, but it isn't? In "spi.h" I see > > "dma_alignment" that claims to be exactly what you need. As far as I > > can tell, though, the core doesn't use this? ...so I'm kinda confused. > > As far as I can tell this doesn't do anything and thus anyone setting > > it today is broken? > > SPI consumers should only be providing dmaable buffers.
Ah, I think I see.
1. In "struct spi_transfer" the @tx_buf and @rx_buf are documented to have "dma-safe memory".
2. On ARM64 anyway, I see "ARCH_DMA_MINALIGN" is 128.
So there is no reason to do any special rules to force alignment to 32-bytes because that's already guaranteed. Presumably that means you can drop a whole pile of code and things will still work fine.
-Doug
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