Re: [PATCH] spi: dw-dma: Fix Tx DMA channel working too fast

[Mark Brown <broonie@xxxxxxxxxx>]

On Tue, 21 Jul 2020 23:39:51 +0300, Serge Semin wrote:
> It turns out having a Rx DMA channel serviced with higher priority than
> a Tx DMA channel is not enough to provide a well balanced DMA-based SPI
> transfer interface. There might still be moments when the Tx DMA channel
> is occasionally handled faster than the Rx DMA channel. That in its turn
> will eventually cause the SPI Rx FIFO overflow if SPI bus speed is high
> enough to fill the SPI Rx FIFO in before it's cleared by the Rx DMA
> channel. That's why having the DMA-based SPI Tx interface too optimized
> is the errors prone, so the commit 0b2b66514fc9 ("spi: dw: Use DMA max
> burst to set the request thresholds") though being perfectly normal from
> the standard functionality point of view implicitly introduced the problem
> described above. In order to fix that the Tx DMA activity is intentionally
> slowed down by limiting the SPI Tx FIFO depth with a value twice bigger
> than the Tx burst length calculated earlier by the
> dw_spi_dma_maxburst_init() method.

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: dw-dma: Fix Tx DMA channel working too fast
      commit: affe93dd5b35bb0e7b0aa0505ae432dd0ac72c3f

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

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Thanks,
Mark