[PATCH] drm/amdgpu: add dce6 drm_panic support

[Lu Yao]

On 2024/8/5 17:25, Jocelyn Falempe wrote:
>
>
> On 02/08/2024 11:39, Christian König wrote:
>> 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 at kylinos.cn>
>>> ---
>>>   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.
>
> For the CPU accessible issue, Christian mentioned there was a debug 
> interface on AMD GPU that can be used, to work around this:
>
> https://lore.kernel.org/dri-devel/0baabe1f-8924-2c9a-5cd4-59084a37dbb2@gmail.com/ 
> and 
> https://lore.kernel.org/dri-devel/d233c376-ed07-2127-6084-8292d313dac7@amd.com/
>
> And you will need to use the scanout_buffer->set_pixel() callback to 
> write the pixels one by one, similar to what I've tried for nouveau with
> https://patchwork.freedesktop.org/series/133963/
>
> For the tiling format, the problem is that it is internal to the GPU, 
> and currently the driver don't know which tiling format is being used.
>
> It might be possible to disable tiling and compression, but it 
> requires some internal DC knowledge:
> https://lore.kernel.org/dri-devel/f76a3297-7d63-8615-45c5-47f02b64a1d5@amd.com/ 
>
>
> Best regards,

>From the discussion provided, it is difficult to implement this feature without the relevant data book and knowledge.(Whether how tiled memory storage, or how to disable tiling of DC)

It looks like I'll just have to wait for AMD engineers to implement this.

Thanks a lot,
Lu Yao