Re: [PATCH v3] drm/ast: add dmabuf/prime buffer sharing support

From: Thomas Zimmermann
Date: Mon Sep 05 2022 - 05:19:26 EST

Hi,

I've been on vacation. Sorry for the late reply.

I have plans to replace ast's memory manager with the GEM SHMEM helpers. These already support PRIME buffer sharing and the usecase you describe. I also consider the GEM VRAM helpers used by ast as deprecated. There's no benefit over SHMEM helpers, except with the bochs driver. So whatever we merge here, might not live for too long.

Am 01.09.22 um 14:44 schrieb oushixiong:

This patch adds ast specific codes for DRM prime feature, this is to
allow for offloading of rending in one direction and outputs in other.

This patch is designed to solve the problem that the AST is not displayed
when the server plug in a discrete graphics card at the same time.
We call the dirty callback function to copy the rendering results of the
discrete graphics card to the ast side by dma-buf.

I assume that userspace guarantees that both, ASPEED and discrete device, are set the the same display resolution?


v1->v2:
- Fix the comment.
v2->v3:
- we remove the gem_prime_import_sg_table callback and use the
gem_prime_import callback, because it just map and access the buffer
with the CPU. and do not to pin the buffer.

Signed-off-by: oushixiong <oushixiong@xxxxxxxxxx>
Acked-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/gpu/drm/ast/ast_drv.c | 27 +++++++
drivers/gpu/drm/ast/ast_mode.c | 125 ++++++++++++++++++++++++++++++++-
2 files changed, 151 insertions(+), 1 deletion(-)

There's nothing specifically to AST here. Could this be build on GEM VRAM helpers instead? A handful of other drivers should then be able to use the functionality.


diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
index 7465c4f0156a..fd3c4bad2eb4 100644
--- a/drivers/gpu/drm/ast/ast_drv.c
+++ b/drivers/gpu/drm/ast/ast_drv.c
@@ -28,6 +28,7 @@
#include <linux/module.h>
#include <linux/pci.h>
+#include <linux/dma-buf.h>

Sort alphabetically please.

#include <drm/drm_aperture.h>
#include <drm/drm_atomic_helper.h>
@@ -50,6 +51,29 @@ module_param_named(modeset, ast_modeset, int, 0400);
DEFINE_DRM_GEM_FOPS(ast_fops);
+static struct drm_gem_object *ast_gem_prime_import(struct drm_device *dev,
+ struct dma_buf *dma_buf)
+{
+ struct drm_gem_vram_object *gbo;
+
+ gbo = drm_gem_vram_of_gem(dma_buf->priv);
+ if (gbo->bo.base.dev == dev) {
+ /*
+ * Importing dmabuf exported from out own gem increases
+ * refcount on gem itself instead of f_count of dmabuf.
+ */
+ drm_gem_object_get(&gbo->bo.base);
+ return &gbo->bo.base;
+ }
+
+ gbo = drm_gem_vram_create(dev, dma_buf->size, 0);
+ if (IS_ERR(gbo))
+ return NULL;
+
+ get_dma_buf(dma_buf);
+ return &gbo->bo.base;
+}
+
static const struct drm_driver ast_driver = {
.driver_features = DRIVER_ATOMIC |
DRIVER_GEM |
@@ -63,6 +87,9 @@ static const struct drm_driver ast_driver = {
.minor = DRIVER_MINOR,
.patchlevel = DRIVER_PATCHLEVEL,
+ .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
+ .gem_prime_import = ast_gem_prime_import,
+
DRM_GEM_VRAM_DRIVER
};
diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 45b56b39ad47..65a4342c5622 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -48,6 +48,8 @@
#include "ast_drv.h"
#include "ast_tables.h"
+MODULE_IMPORT_NS(DMA_BUF);
+
static inline void ast_load_palette_index(struct ast_private *ast,
u8 index, u8 red, u8 green,
u8 blue)
@@ -1535,8 +1537,129 @@ static const struct drm_mode_config_helper_funcs ast_mode_config_helper_funcs =
.atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
};
+static int ast_handle_damage(struct drm_framebuffer *fb, int x, int y,
+ int width, int height)
+{
+ struct drm_gem_vram_object *dst_bo = NULL;
+ void *dst = NULL;
+ int ret = 0, i;
+ unsigned long offset = 0;
+ bool unmap = false;
+ unsigned int bytesPerPixel;
+ struct iosys_map map;
+ struct iosys_map dmabuf_map;
+
+ bytesPerPixel = fb->format->cpp[0];
+
+ if (!fb->obj[0]->dma_buf)
+ return -EINVAL;
+
+ if (!fb->obj[0]->dma_buf->vmap_ptr.vaddr) {
+ ret = dma_buf_vmap(fb->obj[0]->dma_buf, &dmabuf_map);
+ if (ret)
+ return ret;
+ } else
+ dmabuf_map.vaddr = fb->obj[0]->dma_buf->vmap_ptr.vaddr;

It's too late to call dma_buf_vmap() here. The correct place would be drm_plane_helper_funcs.prepare_fb for the vmap and the resulting address would have to be stored in a VRAM plane state. The vunmap call would go into drm_plane_helper_funcs.cleanup_fb.

We already have prepare_fb/cleanup_fb for the VRAM helpers. There's no VRAM-specific plane-state yet.

+
+ dst_bo = drm_gem_vram_of_gem(fb->obj[0]);
+
+ ret = drm_gem_vram_pin(dst_bo, 0);
+ if (ret) {
+ DRM_ERROR("ast_bo_pin failed\n");
+ return ret;
+ }

Like vmap, pinning should be done by the existing prepare_fb helper
drm_gem_vram_plane_helper_prepare_fb().

+
+ if (!dst_bo->map.vaddr) {
+ ret = drm_gem_vram_vmap(dst_bo, &map);
+ if (ret) {
+ drm_gem_vram_unpin(dst_bo);
+ DRM_ERROR("failed to vmap fbcon\n");
+ return ret;
+ }
+ unmap = true;
+ }
+ dst = dst_bo->map.vaddr;
+
+ for (i = y; i < y + height; i++) {
+ offset = i * fb->pitches[0] + (x * bytesPerPixel);
+ memcpy_toio(dst + offset, dmabuf_map.vaddr + offset,
+ width * bytesPerPixel);
+ }

drm_fb_mempy() implements this logic already.

+
+ if (unmap)
+ drm_gem_vram_vunmap(dst_bo, &map);
+
+ drm_gem_vram_unpin(dst_bo);

Cleanup goes into drm_gem_vram_plane_helper_cleanup_fb()

+
+ return 0;
+}
+
+
+static int ast_user_framebuffer_dirty(struct drm_framebuffer *fb,
+ struct drm_file *file,
+ unsigned int flags,
+ unsigned int color,
+ struct drm_clip_rect *clips,
+ unsigned int num_clips)
+{
+ int i, ret = 0;
+
+ drm_modeset_lock_all(fb->dev);
+ if (fb->obj[0]->dma_buf) {
+ ret = dma_buf_begin_cpu_access(fb->obj[0]->dma_buf,
+ DMA_FROM_DEVICE);
+ if (ret)
+ goto unlock;
+ }

This is already available in drm_gem_fb_begin_cpu_access()

+
+ for (i = 0; i < num_clips; i++) {
+ ret = ast_handle_damage(fb, clips[i].x1, clips[i].y1,
+ clips[i].x2 - clips[i].x1, clips[i].y2 - clips[i].y1);
+ if (ret)
+ break;
+ }
+
+ if (fb->obj[0]->dma_buf) {
+ dma_buf_end_cpu_access(fb->obj[0]->dma_buf,
+ DMA_FROM_DEVICE);

That's in drm_gem_fb_end_cpu_access()

+ }
+
+unlock:
+ drm_modeset_unlock_all(fb->dev);
+
+ return ret;
+}
+
+static void ast_user_framebuffer_destroy(struct drm_framebuffer *fb)
+{
+ struct iosys_map dmabuf_map;
+
+ if (fb->obj[0]->dma_buf) {
+ dmabuf_map.is_iomem = fb->obj[0]->dma_buf->vmap_ptr.is_iomem;
+ dmabuf_map.vaddr = fb->obj[0]->dma_buf->vmap_ptr.vaddr;
+ if (dmabuf_map.vaddr)
+ dma_buf_vunmap(fb->obj[0]->dma_buf, &dmabuf_map);
+ }
+
+ drm_gem_fb_destroy(fb);
+}
+
+static const struct drm_framebuffer_funcs ast_gem_fb_funcs_dirtyfb = {
+ .destroy = ast_user_framebuffer_destroy,
+ .create_handle = drm_gem_fb_create_handle,
+ .dirty = ast_user_framebuffer_dirty,
+};
+
+static struct drm_framebuffer *
+ast_gem_fb_create_with_dirty(struct drm_device *dev, struct drm_file *file,
+ const struct drm_mode_fb_cmd2 *mode_cmd)
+{
+ return drm_gem_fb_create_with_funcs(dev, file, mode_cmd,
+ &ast_gem_fb_funcs_dirtyfb);
+}
+
static const struct drm_mode_config_funcs ast_mode_config_funcs = {
- .fb_create = drm_gem_fb_create,
+ .fb_create = ast_gem_fb_create_with_dirty,

AFAICT, the whole framebuffer update code can be solved with existing generic helpers and the VRAM updates I outlined above. As part of ast's atomic update, the displayed data will be updated from the dma-buf-attached external BO.

But as I said, I consider the VRAM helpers a deprecated. And once I moved ast to the SHMEM helpers, the functionality will be there as well.

Best regards
Thomas


.mode_valid = drm_vram_helper_mode_valid,
.atomic_check = drm_atomic_helper_check,
.atomic_commit = drm_atomic_helper_commit,


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--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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