Re: [PATCH] drm/amdgpu: add dce6 drm_panic support

[Christian König]

Am 02.08.24 um 09:17 schrieb Lu Yao:
> Add support for the drm_panic module, which displays a pretty user
> friendly message on the screen when a Linux kernel panic occurs.
>
> Signed-off-by: Lu Yao <yaolu@xxxxxxxxxx>
> ---
> The patch can work properly on the TTY, but after start X, drawn
> image is messy, it looks like the data isn't linearly arranged.
> However at this time 'fb->modifier' is 'DRM_FORMAT_MOD_LINEAR'.
>
> Another difference I found is:
>    For TTY, the amdgpu_bo is created with flag
>    'AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED|AMDGPU_GEM_CREATE_CPU_GTT_USWC|
>    AMDGPU_GEM_CREATE_VRAM_CLEARED|AMDGPU_GEM_CREATE_VRAM_CONTIGUOUS'.
>    For X, the amdgpu_bo is created with flag
>    'AMDGPU_GEM_CREATE_NO_CPU_ACCESS|AMDGPU_GEM_CREATE_CPU_GTT_USWC'
> I try to use same flag for X, it looks like no difference.
>
> Can someone provide some insight into this problem or where I am going
> wrong. Thanks a lot.
>
> Test environment: X86 arch + v6.6 kernel + R7340.
> ---
>   drivers/gpu/drm/amd/amdgpu/dce_v6_0.c | 32 +++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v6_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v6_0.c
> index 05c0df97f01d..12c3801c264a 100644
> --- a/drivers/gpu/drm/amd/amdgpu/dce_v6_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/dce_v6_0.c
> @@ -28,6 +28,8 @@
>   #include <drm/drm_modeset_helper.h>
>   #include <drm/drm_modeset_helper_vtables.h>
>   #include <drm/drm_vblank.h>
> +#include <drm/drm_panic.h>

> +#include "../../drm_internal.h"

Well that this file is named "internal" and not in a common include 
directory is a strong indicator that you should absolutely *not* include 
it in a driver.

>   
>   #include "amdgpu.h"
>   #include "amdgpu_pm.h"
> @@ -2600,6 +2602,35 @@ static const struct drm_crtc_helper_funcs dce_v6_0_crtc_helper_funcs = {
>   	.get_scanout_position = amdgpu_crtc_get_scanout_position,
>   };
>   
> +static int dce_v6_0_drm_primary_plane_get_scanout_buffer(struct drm_plane *plane,
> +							 struct drm_scanout_buffer *sb)
> +{
> +	struct drm_framebuffer *fb;
> +	struct drm_gem_object *obj;
> +	struct amdgpu_bo *abo;
> +	int ret = 0;
> +
> +	if (!plane->fb || plane->fb->modifier != DRM_FORMAT_MOD_LINEAR)
> +		return -ENODEV;
> +
> +	fb = plane->fb;
> +	sb->width = fb->width;
> +	sb->height = fb->height;
> +	sb->format = fb->format;
> +	sb->pitch[0] = fb->pitches[0];
> +
> +	obj = fb->obj[0];
> +	abo = gem_to_amdgpu_bo(obj);
> +	if (!abo || abo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)
> +		return -EINVAL;
> +
> +	return drm_gem_vmap(obj, &sb->map[0]);

Yeah that will almost always not work. Most display buffers are tilled 
and not CPU accessible.

Regards,
Christian.

> +}
> +
> +static const struct drm_plane_helper_funcs dce_v6_0_drm_primary_plane_helper_funcs = {
> +	.get_scanout_buffer = dce_v6_0_drm_primary_plane_get_scanout_buffer
> +};
> +
>   static int dce_v6_0_crtc_init(struct amdgpu_device *adev, int index)
>   {
>   	struct amdgpu_crtc *amdgpu_crtc;
> @@ -2627,6 +2658,7 @@ static int dce_v6_0_crtc_init(struct amdgpu_device *adev, int index)
>   	amdgpu_crtc->encoder = NULL;
>   	amdgpu_crtc->connector = NULL;
>   	drm_crtc_helper_add(&amdgpu_crtc->base, &dce_v6_0_crtc_helper_funcs);
> +	drm_plane_helper_add(amdgpu_crtc->base.primary, &dce_v6_0_drm_primary_plane_helper_funcs);
>   
>   	return 0;
>   }