[PATCH v2] drm/ast: Fix start address computation

[Jammy Huang]

Hello,

The offset given to ast_set_start_address_crt1() should be offset in 
vram. It should 0 now as your patch.

I think it is better to correct it in ast_primary_plane_init() and 
ast_cursor_plane_init() as below.

--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -714,7 +714,7 @@ static int ast_primary_plane_init(struct ast_private 
*ast)
         struct ast_plane *ast_primary_plane = &ast->primary_plane;
         struct drm_plane *primary_plane = &ast_primary_plane->base;
         void __iomem *vaddr = ast->vram;
-       u64 offset = ast->vram_base;
+       u64 offset = 0;
         unsigned long cursor_size = roundup(AST_HWC_SIZE + 
AST_HWC_SIGNATURE_SIZE, PAGE_SIZE);
         unsigned long size = ast->vram_fb_available - cursor_size;
         int ret;
@@ -972,7 +972,7 @@ static int ast_cursor_plane_init(struct ast_private 
*ast)
                 return -ENOMEM;

         vaddr = ast->vram + ast->vram_fb_available - size;
-       offset = ast->vram_base + ast->vram_fb_available - size;
+       offset = st->vram_fb_available - size;

On 2023/2/9 下午 05:12, Jocelyn Falempe wrote:
> During the driver conversion to shmem, the start address for the
> scanout buffer was set to the base PCI address.
> In most cases it works because only the lower 24bits are used, and
> due to alignment it was almost always 0.
> But on some unlucky hardware, it's not the case, and some unitilized
> memory is displayed on the BMC.
> With shmem, the primary plane is always at offset 0 in GPU memory.
>
> Tested on a sr645 affected by this bug.
>
> Fixes: f2fa5a99ca81 ("drm/ast: Convert ast to SHMEM")
> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
> ---
>   drivers/gpu/drm/ast/ast_mode.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index c7443317c747..54deb29bfeb3 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -681,7 +681,8 @@ static void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
>   	if (!old_fb || old_fb->pitches[0] != fb->pitches[0])
>   		ast_set_offset_reg(ast, fb);
>   	if (!old_fb) {
> -		ast_set_start_address_crt1(ast, (u32)ast_plane->offset);
> +		/* with shmem, the primary plane is always at offset 0 */
> +		ast_set_start_address_crt1(ast, 0);
>   		ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x00);
>   	}
>   }

-- 
Best Regards
Jammy