Virtualization - Feb 2021 - [PATCH 09/10] drm/qxl: map/unmap framebuffers in prepare_fb+cleanup_fb callbacks.

Am 16.02.21 um 14:27 schrieb Thomas Zimmermann:
> Hi
> 
> this is a shadow-buffered plane. Did you consider using the new helpers 
> for shadow-buffered planes? They will map the user BO for you and 
> provide the mapping in the plane state.
> 
>  From there, you should implement your own plane state on top of struct 
> drm_shadow_plane_state, and also move all the other allocations and 
> vmaps into prepare_fb and cleanup_fb. Most of this is not actually 
> allowed in commit tails. All we'd have to do is to export the reset, 
> duplicate and destroy code; similar to what 
> __drm_atomic_helper_plane_reset() does.
AFAICT the cursor_bo is used to implement double buffering for the 
cursor image.

Ideally, you can do what ast does: pre-allocate/vmap 2 BOs at the end of 
the vram. Then pageflip between them in atomic_update(). Resolves all 
the allocation and mapping headaches.

Best regards
Thomas
> 
> Best regards
> Thomas
> 
> 
> Am 16.02.21 um 12:37 schrieb Gerd Hoffmann:
>> We don't have to map in atomic_update callback then,
>> making locking a bit less complicated.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
>> ---
>> ? drivers/gpu/drm/qxl/qxl_display.c | 14 +++++---------
>> ? 1 file changed, 5 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/qxl/qxl_display.c 
>> b/drivers/gpu/drm/qxl/qxl_display.c
>> index 7500560db8e4..39b8c5116d34 100644
>> --- a/drivers/gpu/drm/qxl/qxl_display.c
>> +++ b/drivers/gpu/drm/qxl/qxl_display.c
>> @@ -584,7 +584,6 @@ static void qxl_cursor_atomic_update(struct 
>> drm_plane *plane,
>> ????? struct drm_gem_object *obj;
>> ????? struct qxl_bo *cursor_bo = NULL, *user_bo = NULL, *old_cursor_bo 
>> = NULL;
>> ????? int ret;
>> -??? struct dma_buf_map user_map;
>> ????? struct dma_buf_map cursor_map;
>> ????? void *user_ptr;
>> ????? int size = 64*64*4;
>> @@ -599,11 +598,8 @@ static void qxl_cursor_atomic_update(struct 
>> drm_plane *plane,
>> ????????? obj = fb->obj[0];
>> ????????? user_bo = gem_to_qxl_bo(obj);
>> -??????? /* pinning is done in the prepare/cleanup framevbuffer */
>> -??????? ret = qxl_bo_kmap_locked(user_bo, &user_map);
>> -??????? if (ret)
>> -??????????? goto out_free_release;
>> -??????? user_ptr = user_map.vaddr; /* TODO: Use mapping abstraction 
>> properly */
>> +??????? /* mapping is done in the prepare/cleanup framevbuffer */
>> +??????? user_ptr = user_bo->map.vaddr; /* TODO: Use mapping 
>> abstraction properly */
>> ????????? ret = qxl_alloc_bo_reserved(qdev, release,
>> ????????????????????????? sizeof(struct qxl_cursor) + size,
>> @@ -639,7 +635,6 @@ static void qxl_cursor_atomic_update(struct 
>> drm_plane *plane,
>> ????????? cursor->chunk.data_size = size;
>> ????????? memcpy(cursor->chunk.data, user_ptr, size);
>> ????????? qxl_bo_kunmap_locked(cursor_bo);
>> -??????? qxl_bo_kunmap_locked(user_bo);
>> ????????? cmd = (struct qxl_cursor_cmd *) qxl_release_map(qdev,
release);
>> ????????? cmd->u.set.visible = 1;
>> @@ -778,6 +773,7 @@ static int qxl_plane_prepare_fb(struct drm_plane 
>> *plane,
>> ????? struct drm_gem_object *obj;
>> ????? struct qxl_bo *user_bo;
>> ????? struct qxl_surface surf;
>> +??? struct dma_buf_map unused;
>> ????? if (!new_state->fb)
>> ????????? return 0;
>> @@ -815,7 +811,7 @@ static int qxl_plane_prepare_fb(struct drm_plane 
>> *plane,
>> ????????? }
>> ????? }
>> -??? return qxl_bo_pin(user_bo);
>> +??? return qxl_bo_kmap(user_bo, &unused);
>> ? }
>> ? static void qxl_plane_cleanup_fb(struct drm_plane *plane,
>> @@ -834,7 +830,7 @@ static void qxl_plane_cleanup_fb(struct drm_plane 
>> *plane,
>> ????? obj = old_state->fb->obj[0];
>> ????? user_bo = gem_to_qxl_bo(obj);
>> -??? qxl_bo_unpin(user_bo);
>> +??? qxl_bo_kunmap(user_bo);
>> ????? if (old_state->fb != plane->state->fb &&
user_bo->shadow) {
>> ????????? qxl_bo_unpin(user_bo->shadow);
>>
> 
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 N?rnberg, Germany
(HRB 36809, AG N?rnberg)
Gesch?ftsf?hrer: Felix Imend?rffer

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On Tue, Feb 16, 2021 at 02:46:21PM +0100, Thomas Zimmermann
wrote:
> 
> 
> Am 16.02.21 um 14:27 schrieb Thomas Zimmermann:
> > Hi
> > 
> > this is a shadow-buffered plane. Did you consider using the new
helpers
> > for shadow-buffered planes? They will map the user BO for you and
> > provide the mapping in the plane state.
> > 
> >  From there, you should implement your own plane state on top of
struct
> > drm_shadow_plane_state, and also move all the other allocations and
> > vmaps into prepare_fb and cleanup_fb. Most of this is not actually
> > allowed in commit tails. All we'd have to do is to export the
reset,
> > duplicate and destroy code; similar to what
> > __drm_atomic_helper_plane_reset() does.
> 
> AFAICT the cursor_bo is used to implement double buffering for the cursor
> image.
> 
> Ideally, you can do what ast does: pre-allocate/vmap 2 BOs at the end of
the
> vram. Then pageflip between them in atomic_update(). Resolves all the
> allocation and mapping headaches.
Just waded through the ast patches.

It is not that simple for qxl.  You have to send a command to the
virtualization host and take care of the host accessing that memory
when processing the command, so you can't reuse the memory until the
host signals it is fine to do so.

But, yes, it should be possible to handle cursor_bo creation in
prepare_fb without too much effort.

take care,
  Gerd