On Tue, Jun 24, 2014 at 7:55 PM, Alexandre Courbot <acourbot@xxxxxxxxxx> wrote: > On 06/24/2014 07:33 PM, Alexandre Courbot wrote: >> >> On 06/24/2014 07:02 PM, Russell King - ARM Linux wrote: >>> >>> On Tue, Jun 24, 2014 at 06:54:26PM +0900, Alexandre Courbot wrote: >>>> >>>> From: Lucas Stach <dev@xxxxxxxxxx> >>>> >>>> On architectures for which access to GPU memory is non-coherent, >>>> caches need to be flushed and invalidated explicitly at the >>>> appropriate places. Introduce two small helpers to make things >>>> easy for TTM-based drivers. >>> >>> >>> Have you run this with DMA API debugging enabled? I suspect you haven't, >>> and I recommend that you do. >> >> >> # cat /sys/kernel/debug/dma-api/error_count >> 162621 >> >> (╯°□°）╯︵ ┻━┻) > > > *puts table back on its feet* > > So, yeah - TTM memory is not allocated using the DMA API, hence we cannot > use the DMA API to sync it. Thanks Russell for pointing it out. > > The only alternative I see here is to flush the CPU caches when syncing for > the device, and invalidate them for the other direction. Of course if the > device has caches on its side as well the opposite operation must also be > done for it. Guess the only way is to handle it all by ourselves here. :/ ... and it really sucks. Basically if we cannot use the DMA API here we will lose the convenience of having a portable API that does just the right thing for the underlying platform. Without it we would have to duplicate arm_iommu_sync_single_for_cpu/device() and we would only have support for ARM. The usage of the DMA API that we are doing might be illegal, but in essence it does exactly what we need - at least for ARM. What are the alternatives? -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
