Am 24.11.20 um 10:16 schrieb Thomas Zimmermann:
Hi Christian
Am 16.11.20 um 12:28 schrieb Christian König:
Am 13.11.20 um 08:59 schrieb Thomas Zimmermann:
Hi Christian
Am 12.11.20 um 18:16 schrieb Christian König:
Am 12.11.20 um 14:21 schrieb Thomas Zimmermann:
In order to avoid eviction of vmap'ed buffers, pin them in their GEM
object's vmap implementation. Unpin them in the vunmap
implementation.
This is needed to make generic fbdev support work reliably. Without,
the buffer object could be evicted while fbdev flushed its shadow
buffer.
In difference to the PRIME pin/unpin functions, the vmap code does
not
modify the BOs prime_shared_count, so a vmap-pinned BO does not
count as
shared.
The actual pin location is not important as the vmap call returns
information on how to access the buffer. Callers that require a
specific location should explicitly pin the BO before vmapping it.
Well is the buffer supposed to be scanned out?
No, not by the fbdev helper.
Ok in this case that should work.
If yes then the pin location is actually rather important since the
hardware can only scan out from VRAM.
For relocatable BOs, fbdev uses a shadow buffer that makes all any
relocation transparent to userspace. It flushes the shadow fb into the
BO's memory if there are updates. The code is in
drm_fb_helper_dirty_work(). [1] During the flush operation, the vmap
call now pins the BO to wherever it is. The actual location does not
matter. It's vunmap'ed immediately afterwards.
The problem is what happens when it is prepared for scanout, but
can't be moved to VRAM because it is vmapped?
When the shadow is never scanned out that isn't a problem, but we
need to keep that in mind.
I'd like ask for your suggestions before sending an update for this
patch.
After the discussion about locking in fbdev, [1] I intended to replace
the pin call with code that acquires the reservation lock.
Yeah, that sounds like a good idea to me as well.
First I wanted to put this into drm_gem_ttm_vmap/vunmap(), but then
wondered why ttm_bo_vmap() doe not acquire the lock internally? I'd
expect that vmap/vunmap are close together and do not overlap for the
same BO.
We have use cases like the following during command submission:
1. lock
2. map
3. copy parts of the BO content somewhere else or patch it with
additional information
4. unmap
5. submit BO to the hardware
6. add hardware fence to the BO to make sure it doesn't move
7. unlock
That use case won't be possible with vmap/vunmap if we move the
lock/unlock into it and I hope to replace the kmap/kunmap functions with
them in the near term.
Otherwise, acquiring the reservation lock would require another
ref-counting variable or per-driver code.
Hui, why that? Just put this into drm_gem_ttm_vmap/vunmap() helper as
you initially planned.
Regards,
Christian.
Best regards
Thomas
[1] https://patchwork.freedesktop.org/patch/401088/?series=83918&rev=1
Regards,
Christian.
For dma-buf sharing, the regular procedure of pin + vmap still apply.
This should always move the BO into GTT-managed memory.
Best regards
Thomas
[1]
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Ftree%2Fdrivers%2Fgpu%2Fdrm%2Fdrm_fb_helper.c%23n432&data=04%7C01%7Cchristian.koenig%40amd.com%7C31b890664ca7429fc45808d887aa0842%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637408511650629569%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=RLauuAuXkcl0rXwWWJ%2FrKP%2BsCr2wAzU1ejGV1bnQ80w%3D&reserved=0
Regards,
Christian.
Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
drivers/gpu/drm/radeon/radeon_gem.c | 51
+++++++++++++++++++++++++++--
1 file changed, 49 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/radeon/radeon_gem.c
b/drivers/gpu/drm/radeon/radeon_gem.c
index d2876ce3bc9e..eaf7fc9a7b07 100644
--- a/drivers/gpu/drm/radeon/radeon_gem.c
+++ b/drivers/gpu/drm/radeon/radeon_gem.c
@@ -226,6 +226,53 @@ static int radeon_gem_handle_lockup(struct
radeon_device *rdev, int r)
return r;
}
+static int radeon_gem_object_vmap(struct drm_gem_object *obj,
struct dma_buf_map *map)
+{
+ static const uint32_t any_domain = RADEON_GEM_DOMAIN_VRAM |
+ RADEON_GEM_DOMAIN_GTT |
+ RADEON_GEM_DOMAIN_CPU;
+
+ struct radeon_bo *bo = gem_to_radeon_bo(obj);
+ int ret;
+
+ ret = radeon_bo_reserve(bo, false);
+ if (ret)
+ return ret;
+
+ /* pin buffer at its current location */
+ ret = radeon_bo_pin(bo, any_domain, NULL);
+ if (ret)
+ goto err_radeon_bo_unreserve;
+
+ ret = drm_gem_ttm_vmap(obj, map);
+ if (ret)
+ goto err_radeon_bo_unpin;
+
+ radeon_bo_unreserve(bo);
+
+ return 0;
+
+err_radeon_bo_unpin:
+ radeon_bo_unpin(bo);
+err_radeon_bo_unreserve:
+ radeon_bo_unreserve(bo);
+ return ret;
+}
+
+static void radeon_gem_object_vunmap(struct drm_gem_object *obj,
struct dma_buf_map *map)
+{
+ struct radeon_bo *bo = gem_to_radeon_bo(obj);
+ int ret;
+
+ ret = radeon_bo_reserve(bo, false);
+ if (ret)
+ return;
+
+ drm_gem_ttm_vunmap(obj, map);
+ radeon_bo_unpin(bo);
+ radeon_bo_unreserve(bo);
+}
+
static const struct drm_gem_object_funcs
radeon_gem_object_funcs = {
.free = radeon_gem_object_free,
.open = radeon_gem_object_open,
@@ -234,8 +281,8 @@ static const struct drm_gem_object_funcs
radeon_gem_object_funcs = {
.pin = radeon_gem_prime_pin,
.unpin = radeon_gem_prime_unpin,
.get_sg_table = radeon_gem_prime_get_sg_table,
- .vmap = drm_gem_ttm_vmap,
- .vunmap = drm_gem_ttm_vunmap,
+ .vmap = radeon_gem_object_vmap,
+ .vunmap = radeon_gem_object_vunmap,
};
/*
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