Messages in this thread | | | Date | Tue, 10 Jan 2017 11:51:33 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2] arm64: do not set dma masks that device connection can't handle |
| |
On Mon, Jan 09, 2017 at 10:30:02AM +0300, Nikita Yushchenko wrote: > It is possible that device is capable of 64-bit DMA addresses, and > device driver tries to set wide DMA mask, but bridge or bus used to > connect device to the system can't handle wide addresses. > > With swiotlb, memory above 4G still can be used by drivers for streaming > DMA, but *dev->mask and dev->dma_coherent_mask must still keep values > that hardware handles physically. > > This patch enforces that. Based on original version by > Arnd Bergmann <arnd@arndb.de>, extended with coherent mask hadnling. > > Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com> > CC: Arnd Bergmann <arnd@arndb.de> > --- > Changes since v1: > - fixed issues noted by Sergei Shtylyov <sergei.shtylyov@cogentembedded.com> > - save mask, not size > - remove doube empty line > > arch/arm64/Kconfig | 3 +++ > arch/arm64/include/asm/device.h | 1 + > arch/arm64/mm/dma-mapping.c | 51 +++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 55 insertions(+)
I still don't think this patch is general enough. The problem you're seeing with swiotlb seems to be exactly the same problem reported by Feng Kan over at:
http://lkml.kernel.org/r/CAL85gmA_SSCwM80TKdkZqEe+S1beWzDEvdki1kpkmUTDRmSP7g@mail.gmail.com
[read on; it was initially thought to be a hardware erratum, but it's actually the inability to restrict the DMA mask of the endpoint that's the problem]
The point here is that an IOMMU doesn't solve your issue, and the IOMMU-backed DMA ops need the same treatment. In light of that, it really feels to me like the DMA masks should be restricted in of_dma_configure so that the parent mask is taken into account there, rather than hook into each set of DMA ops to intercept set_dma_mask. We'd still need to do something to stop dma_set_mask widening the mask if it was restricted by of_dma_configure, but I think Robin (cc'd) was playing with that.
Will
| |