Am Dienstag, den 24.06.2014, 14:27 +0200 schrieb Maarten Lankhorst: > 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? :-) Actually TTM already has a page alloc backend using the DMA API. It's just not used for the standard case right now. I would argue that we should just use this page allocator (which has the side effect of getting pages from CMA if available -> you are actually free to change the caching) and do away with the other allocator in the ARM case. Regards, Lucas -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- 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
