Re: [PATCH] drm/amdgpu: add force_sg_display module parameter

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 24.01.23 um 16:13 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.

We tried to avoid that very hard the last time the idea came up. 
Generally I don't think that this is something end users should mess with.

It's certainly useful for internal testing, but I think educating 
everybody how to change a define before compiling the driver should be 
the better approach.

Regards,
Christian.

>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> ---
>   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 |  4 ++++
>   3 files changed, 18 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 a75dba2caeca..bc0eaf2330f2 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -942,6 +942,18 @@ 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 2d237f3d3a2e..78dc5d63a6dd 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -1515,6 +1515,10 @@ 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 (amdgpu_force_sg_display &&
> +	    (adev->asic_type >= CHIP_CARRIZO) &&
> +	    (adev->flags & AMD_IS_APU))
> +		domain = AMDGPU_GEM_DOMAIN_GTT;
>   	return domain;
>   }
>