[PATCH 8/8] drm/ast: Avoid reprogramming primary-plane scanout address

[Jocelyn Falempe]

On 10/10/2022 12:36, Thomas Zimmermann wrote:
> Some AST-based BMCs stop display output for up to 5 seconds after
> reprogramming the scanout address. As the address is fixed, avoid
> re-setting the address' value.
> 
> Reported-by: Jocelyn Falempe <jfalempe at redhat.com>
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>   drivers/gpu/drm/ast/ast_mode.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 1b991658290b..54a9643d86ce 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -672,9 +672,17 @@ static void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
>   	}
>   
>   	ast_set_offset_reg(ast, fb);
> -	ast_set_start_address_crt1(ast, (u32)ast_plane->offset);
>   
> -	ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x00);
> +	/*
> +	 * Some BMCs stop scanning out the video signal after the driver
> +	 * reprogrammed the scanout address. This stalls display output
> +	 * for several seconds and makes the display unusable. Therefore
> +	 * only reprogram the address after enabling the plane.
> +	 */
> +	if (!old_fb && fb) {
> +		ast_set_start_address_crt1(ast, (u32)ast_plane->offset);
> +		ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x00);
> +	}
>   }

I've tested the series, and BMC is still very slow with Gnome/Wayland.

It's because ast_set_offset_reg() also trigger a 5s freeze of the BMC.

I added this, and it works well:

if (!old_fb || old_fb->pitches[0] != fb->pitches[0])
     ast_set_offset_reg(ast, fb);


>   
>   static void ast_primary_plane_helper_atomic_disable(struct drm_plane *plane,




-- 

Jocelyn