[RFC PATCH] drm/amdgpu: add force_sg_display module parameter (v2)

[Christian König]

Am 27.01.23 um 18:51 schrieb Alex Deucher:
> Add a module parameter to force sg (scatter/gather) display
> on APUs.  Normally we allow displays in both VRAM and GTT,
> but this option forces displays into GTT so we can explicitly
> test more scenarios with GTT.

I'm still absolutely not keen to add module parameters for internal testing.

Even with tainting the kernel this is not something we should allow end 
users to do.

Christian.

>
> v2: fix checks
>
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> ---
>
> For reference since the original patch was buggy.
>
>   drivers/gpu/drm/amd/amdgpu/amdgpu.h        |  2 ++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    | 12 ++++++++++++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c |  3 +++
>   3 files changed, 17 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index 872450a3a164..73d0a0807138 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -244,6 +244,8 @@ extern int amdgpu_num_kcq;
>   #define AMDGPU_VCNFW_LOG_SIZE (32 * 1024)
>   extern int amdgpu_vcnfw_log;
>   
> +extern int amdgpu_force_sg_display;
> +
>   #define AMDGPU_VM_MAX_NUM_CTX			4096
>   #define AMDGPU_SG_THRESHOLD			(256*1024*1024)
>   #define AMDGPU_DEFAULT_GTT_SIZE_MB		3072ULL /* 3GB by default */
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index 4cf2028b5235..c8975c2da853 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -943,6 +943,18 @@ MODULE_PARM_DESC(smu_pptable_id,
>   	"specify pptable id to be used (-1 = auto(default) value, 0 = use pptable from vbios, > 0 = soft pptable id)");
>   module_param_named(smu_pptable_id, amdgpu_smu_pptable_id, int, 0444);
>   
> +/**
> + * DOC: force_sg_display (int)
> + * Force display buffers into GTT (scatter/gather) memory for APUs.
> + * This is used to force GTT only for displays rather than displaying from
> + * either VRAM (carve out) or GTT.
> + *
> + * Defaults to 0, or disabled.
> + */
> +int amdgpu_force_sg_display;
> +MODULE_PARM_DESC(force_sg_display, "Force S/G display (0 = off (default), 1 = force display to use GTT) ");
> +module_param_named(force_sg_display, amdgpu_force_sg_display, int, 0444);
> +
>   /* These devices are not supported by amdgpu.
>    * They are supported by the mach64, r128, radeon drivers
>    */
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index 981010de0a28..840190dd78e4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -1516,6 +1516,9 @@ uint32_t amdgpu_bo_get_preferred_domain(struct amdgpu_device *adev,
>   		if (adev->gmc.real_vram_size <= AMDGPU_SG_THRESHOLD)
>   			domain = AMDGPU_GEM_DOMAIN_GTT;
>   	}
> +	if ((domain == (AMDGPU_GEM_DOMAIN_VRAM | AMDGPU_GEM_DOMAIN_GTT)) &&
> +	    amdgpu_force_sg_display && adev->mode_info.gpu_vm_support)
> +		domain = AMDGPU_GEM_DOMAIN_GTT;
>   	return domain;
>   }
>