On Wed, Jan 17, 2018 at 09:31:05AM +0100, Daniel Vetter wrote:
> On Tue, Jan 16, 2018 at 04:35:58PM -0800, Gurchetan Singh wrote:
> > The DMA API can be used to flush scatter gather tables and physical
> > pages on ARM devices.
> >
> > Signed-off-by: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_cache.c | 17 +++++++++++++++++
> > drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 7 ++-----
> > drivers/gpu/drm/tegra/gem.c | 6 +-----
> > 3 files changed, 20 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
> > index 3d2bb9d71a60..98d6ebb40e96 100644
> > --- a/drivers/gpu/drm/drm_cache.c
> > +++ b/drivers/gpu/drm/drm_cache.c
> > @@ -105,6 +105,18 @@ drm_flush_pages(struct device *dev, struct page *pages[],
> > (unsigned long)page_virtual + PAGE_SIZE);
> > kunmap_atomic(page_virtual);
> > }
> > +#elif defined(CONFIG_ARM) || defined(CONFIG_ARM64)
> > + unsigned long i;
> > + dma_addr_t dma_handle;
> > +
> > + if (!dev)
> > + return;
> > +
> > + for (i = 0; i < num_pages; i++) {
> > + dma_handle = phys_to_dma(drm->dev, page_to_phys(pages[i]));
> > + dma_sync_single_for_device(dev, dma_handle, PAGE_SIZE,
> > + DMA_TO_DEVICE);
>
> Erm no. These functions here are super-low-level functions used by drivers
> which know exactly what they're doing. Which is reimplementing half of the
> dma api behind the dma api's back because the dma api just isn't quite
> sufficient for implementing fast gpu drivers.
This isn't obvious from reading the docs, and doubly confusing when reading the
TODOs in the individual drivers. I don't think it's reasonable to assume
everyone (especially first time contributors!) will know this.
>
> If all you end up doing is calling the dma api again, then pls just call
> it directly.
Given that some drivers already midlayer the flush, I don't think it's wrong to
provide "dumb" default behavior so drivers don't need to worry about knowing
exactly what they're doing.
>
> And just to make it clear: I'd be perfectly fine with adding arm support
> here, but then it'd need to directly flush cpu caches and bypass the dma
> api. Otherwise this is pointless.
I don't really have skin in this game, but I think providing one call that works
across all platforms is pretty nice.
Sean
> -Daniel
>
> > + }
> > #else
> > pr_err("Architecture has no drm_cache.c support\n");
> > WARN_ON_ONCE(1);
> > @@ -136,6 +148,11 @@ drm_flush_sg(struct device *dev, struct sg_table *st)
> >
> > if (wbinvd_on_all_cpus())
> > pr_err("Timed out waiting for cache flush\n");
> > +#elif defined(CONFIG_ARM) || defined(CONFIG_ARM64)
> > + if (!dev)
> > + return;
> > +
> > + dma_sync_sg_for_device(dev, st->sgl, st->nents, DMA_TO_DEVICE);
> > #else
> > pr_err("Architecture has no drm_cache.c support\n");
> > WARN_ON_ONCE(1);
> > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > index 8ac7eb25e46d..0157f90b5d10 100644
> > --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
> > @@ -14,6 +14,7 @@
> >
> > #include <drm/drm.h>
> > #include <drm/drmP.h>
> > +#include <drm/drm_cache.h>
> > #include <drm/drm_gem.h>
> > #include <drm/drm_vma_manager.h>
> > #include <linux/iommu.h>
> > @@ -99,15 +100,11 @@ static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj)
> > /*
> > * Fake up the SG table so that dma_sync_sg_for_device() can be used
> > * to flush the pages associated with it.
> > - *
> > - * TODO: Replace this by drm_flush_sg() once it can be implemented
> > - * without relying on symbols that are not exported.
> > */
> > for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->nents, i)
> > sg_dma_address(s) = sg_phys(s);
> >
> > - dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents,
> > - DMA_TO_DEVICE);
> > + drm_flush_sg(drm->dev, rk_obj->sgt);
> >
> > return 0;
> >
> > diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> > index ab1e53d434e8..9945fd2f6bd6 100644
> > --- a/drivers/gpu/drm/tegra/gem.c
> > +++ b/drivers/gpu/drm/tegra/gem.c
> > @@ -230,15 +230,11 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
> > /*
> > * Fake up the SG table so that dma_sync_sg_for_device() can be used
> > * to flush the pages associated with it.
> > - *
> > - * TODO: Replace this by drm_clflash_sg() once it can be implemented
> > - * without relying on symbols that are not exported.
> > */
> > for_each_sg(bo->sgt->sgl, s, bo->sgt->nents, i)
> > sg_dma_address(s) = sg_phys(s);
> >
> > - dma_sync_sg_for_device(drm->dev, bo->sgt->sgl, bo->sgt->nents,
> > - DMA_TO_DEVICE);
> > + drm_flush_sg(drm->dev, bo->sgt);
> >
> > return 0;
> >
> > --
> > 2.13.5
> >
> > _______________________________________________
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> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> _______________________________________________
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> dri-devel@xxxxxxxxxxxxxxxxxxxxx
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--
Sean Paul, Software Engineer, Google / Chromium OS
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