op 24-06-14 14:23, Alexandre Courbot schreef: > 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? Convert TTM to use the dma api? :-) ~Maarten -- 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
