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    SubjectRe: [PATCH AUTOSEL 5.2 42/76] drm/msm: stop abusing dma_map/unmap for cache
    Hi Sasha,

    It's probably best *not* to backport this patch.. drm/msm abuses the
    DMA API in a way that it is not intended be used, to work around the
    lack of cache sync API exported to kernel modules on arm/arm64. I
    couldn't really guarantee that this patch does the right thing on
    older versions of DMA API, so best to leave things as they were.

    BR,
    -R

    On Fri, Aug 2, 2019 at 6:21 AM Sasha Levin <sashal@kernel.org> wrote:
    >
    > From: Rob Clark <robdclark@chromium.org>
    >
    > [ Upstream commit 0036bc73ccbe7e600a3468bf8e8879b122252274 ]
    >
    > Recently splats like this started showing up:
    >
    > WARNING: CPU: 4 PID: 251 at drivers/iommu/dma-iommu.c:451 __iommu_dma_unmap+0xb8/0xc0
    > Modules linked in: ath10k_snoc ath10k_core fuse msm ath mac80211 uvcvideo cfg80211 videobuf2_vmalloc videobuf2_memops vide
    > CPU: 4 PID: 251 Comm: kworker/u16:4 Tainted: G W 5.2.0-rc5-next-20190619+ #2317
    > Hardware name: LENOVO 81JL/LNVNB161216, BIOS 9UCN23WW(V1.06) 10/25/2018
    > Workqueue: msm msm_gem_free_work [msm]
    > pstate: 80c00005 (Nzcv daif +PAN +UAO)
    > pc : __iommu_dma_unmap+0xb8/0xc0
    > lr : __iommu_dma_unmap+0x54/0xc0
    > sp : ffff0000119abce0
    > x29: ffff0000119abce0 x28: 0000000000000000
    > x27: ffff8001f9946648 x26: ffff8001ec271068
    > x25: 0000000000000000 x24: ffff8001ea3580a8
    > x23: ffff8001f95ba010 x22: ffff80018e83ba88
    > x21: ffff8001e548f000 x20: fffffffffffff000
    > x19: 0000000000001000 x18: 00000000c00001fe
    > x17: 0000000000000000 x16: 0000000000000000
    > x15: ffff000015b70068 x14: 0000000000000005
    > x13: 0003142cc1be1768 x12: 0000000000000001
    > x11: ffff8001f6de9100 x10: 0000000000000009
    > x9 : ffff000015b78000 x8 : 0000000000000000
    > x7 : 0000000000000001 x6 : fffffffffffff000
    > x5 : 0000000000000fff x4 : ffff00001065dbc8
    > x3 : 000000000000000d x2 : 0000000000001000
    > x1 : fffffffffffff000 x0 : 0000000000000000
    > Call trace:
    > __iommu_dma_unmap+0xb8/0xc0
    > iommu_dma_unmap_sg+0x98/0xb8
    > put_pages+0x5c/0xf0 [msm]
    > msm_gem_free_work+0x10c/0x150 [msm]
    > process_one_work+0x1e0/0x330
    > worker_thread+0x40/0x438
    > kthread+0x12c/0x130
    > ret_from_fork+0x10/0x18
    > ---[ end trace afc0dc5ab81a06bf ]---
    >
    > Not quite sure what triggered that, but we really shouldn't be abusing
    > dma_{map,unmap}_sg() for cache maint.
    >
    > Cc: Stephen Boyd <sboyd@kernel.org>
    > Tested-by: Stephen Boyd <swboyd@chromium.org>
    > Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
    > Signed-off-by: Rob Clark <robdclark@chromium.org>
    > Signed-off-by: Sean Paul <seanpaul@chromium.org>
    > Link: https://patchwork.freedesktop.org/patch/msgid/20190630124735.27786-1-robdclark@gmail.com
    > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > ---
    > drivers/gpu/drm/msm/msm_gem.c | 4 ++--
    > 1 file changed, 2 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
    > index 49a019939ccdc..a3b5fe1a13944 100644
    > --- a/drivers/gpu/drm/msm/msm_gem.c
    > +++ b/drivers/gpu/drm/msm/msm_gem.c
    > @@ -97,7 +97,7 @@ static struct page **get_pages(struct drm_gem_object *obj)
    > * because display controller, GPU, etc. are not coherent:
    > */
    > if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
    > - dma_map_sg(dev->dev, msm_obj->sgt->sgl,
    > + dma_sync_sg_for_device(dev->dev, msm_obj->sgt->sgl,
    > msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    > }
    >
    > @@ -127,7 +127,7 @@ static void put_pages(struct drm_gem_object *obj)
    > * GPU, etc. are not coherent:
    > */
    > if (msm_obj->flags & (MSM_BO_WC|MSM_BO_UNCACHED))
    > - dma_unmap_sg(obj->dev->dev, msm_obj->sgt->sgl,
    > + dma_sync_sg_for_cpu(obj->dev->dev, msm_obj->sgt->sgl,
    > msm_obj->sgt->nents,
    > DMA_BIDIRECTIONAL);
    >
    > --
    > 2.20.1
    >

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