Hi David, On Mon, Sep 18, 2017 at 05:18:58PM -0700, David Miller wrote: > From: Antoine Tenart <antoine.ten...@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 <stef...@marvell.com> > > Signed-off-by: Antoine Tenart <antoine.ten...@free-electrons.com> > > 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.
That's also the default when the platform does not allocate dma_mask. You have a point, that could be because it's not supported. But I don't know what would be a good check then. > 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. >From what I see in other parts of the kernel, dma_mask points to &coherent_dma_mask by default and having two different values for these two masks isn't a use case for many drivers. Antoine -- Antoine Ténart, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com