Messages in this thread | | | Date | Mon, 18 Sep 2017 17:18:58 -0700 (PDT) | Subject | Re: [PATCH net 1/3] net: mvpp2: fix the dma_mask and coherent_dma_mask settings for PPv2.2 | From | David Miller <> |
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From: Antoine Tenart <antoine.tenart@free-electrons.com> Date: Mon, 18 Sep 2017 15:04:06 +0200
> The dev->dma_mask usually points to dev->coherent_dma_mask. This is an > issue as setting both of them will override the other. This is > problematic here as the PPv2 driver uses a 32-bit-mask for coherent > accesses (txq, rxq, bm) and a 40-bit mask for all other accesses due to > an hardware limitation. > > This can lead to a memory remap for all dma_map_single() calls when > dealing with memory above 4GB. > > Fixes: 2067e0a13cfe ("net: mvpp2: set dma mask and coherent dma mask on PPv2.2") > Reported-by: Stefan Chulski <stefanc@marvell.com> > Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Yikes.
I surrmise that if the platform has made dev->dma_mask point to &dev->coherent_dma_mask, it is because it does not allow the two settings to be set separately.
By rearranging the pointer, you are bypassing that, and probably breaking things or creating a situation that the DMA mapping layer is not expecting.
I want to know more about the situations where dma_mask is set to point to &coherent_dma_mask and how that is supposed to work.
At a minimum this commit log message needs to go into more detail.
Thanks.
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