[PATCH v4] drm/panfrost: Add AFBC_FEATURES parameter

[Steven Price]

On 04/06/2021 14:00, Alyssa Rosenzweig wrote:
> The value of the AFBC_FEATURES register is required by userspace to
> determine AFBC support on Bifrost. A user on our IRC channel (#panfrost)
> reported a workload that raised a fault on one system's Mali G31 but
> worked flawlessly with another system's Mali G31. We determined the
> cause to be missing AFBC support on one vendor's Mali implementation --
> it turns out AFBC is optional on Bifrost!
> 
> Whether AFBC is supported or not is exposed in the AFBC_FEATURES
> register on Bifrost, which reads back as 0 on Midgard. A zero value
> indicates AFBC is fully supported, provided the architecture itself
> supports AFBC, allowing backwards-compatibility with Midgard. Bits 0 and
> 15 indicate that AFBC support is absent for texturing and rendering
> respectively.
> 
> The user experiencing the fault reports that AFBC_FEATURES reads back
> 0x10001 on their system, confirming the architectural lack of AFBC.
> Userspace needs this this parameter to know to disable AFBC on that
                  ^^^^^^^^^
Repeated word ;) But I've fixed that up and pushed it to drm-misc-next.

Thanks,

Steve

> chip, and perhaps others.
> 
> v2: Fix typo from copy-paste fail.
> 
> v3: Bump the UABI version. This commit was cherry-picked from another
> series so chalking this up to a rebase fail.
> 
> Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> Reviewed-by: Steven Price <steven.price at arm.com>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso at collabora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
>  drivers/gpu/drm/panfrost/panfrost_drv.c    | 4 +++-
>  drivers/gpu/drm/panfrost/panfrost_gpu.c    | 1 +
>  drivers/gpu/drm/panfrost/panfrost_regs.h   | 1 +
>  include/uapi/drm/panfrost_drm.h            | 1 +
>  5 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index 597cf1459..f614e9877 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -45,6 +45,7 @@ struct panfrost_features {
>  	u32 thread_max_workgroup_sz;
>  	u32 thread_max_barrier_sz;
>  	u32 coherency_features;
> +	u32 afbc_features;
>  	u32 texture_features[4];
>  	u32 js_features[16];
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index ca07098a6..1596559f3 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -63,6 +63,7 @@ static int panfrost_ioctl_get_param(struct drm_device *ddev, void *data, struct
>  		PANFROST_FEATURE(THREAD_MAX_BARRIER_SZ,
>  				thread_max_barrier_sz);
>  		PANFROST_FEATURE(COHERENCY_FEATURES, coherency_features);
> +		PANFROST_FEATURE(AFBC_FEATURES, afbc_features);
>  		PANFROST_FEATURE_ARRAY(TEXTURE_FEATURES, texture_features, 3);
>  		PANFROST_FEATURE_ARRAY(JS_FEATURES, js_features, 15);
>  		PANFROST_FEATURE(NR_CORE_GROUPS, nr_core_groups);
> @@ -547,6 +548,7 @@ DEFINE_DRM_GEM_FOPS(panfrost_drm_driver_fops);
>   * Panfrost driver version:
>   * - 1.0 - initial interface
>   * - 1.1 - adds HEAP and NOEXEC flags for CREATE_BO
> + * - 1.2 - adds AFBC_FEATURES query
>   */
>  static const struct drm_driver panfrost_drm_driver = {
>  	.driver_features	= DRIVER_RENDER | DRIVER_GEM | DRIVER_SYNCOBJ,
> @@ -559,7 +561,7 @@ static const struct drm_driver panfrost_drm_driver = {
>  	.desc			= "panfrost DRM",
>  	.date			= "20180908",
>  	.major			= 1,
> -	.minor			= 1,
> +	.minor			= 2,
>  
>  	.gem_create_object	= panfrost_gem_create_object,
>  	.prime_handle_to_fd	= drm_gem_prime_handle_to_fd,
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index 2aae636f1..0e70e27fd 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -228,6 +228,7 @@ static void panfrost_gpu_init_features(struct panfrost_device *pfdev)
>  	pfdev->features.thread_max_workgroup_sz = gpu_read(pfdev, GPU_THREAD_MAX_WORKGROUP_SIZE);
>  	pfdev->features.thread_max_barrier_sz = gpu_read(pfdev, GPU_THREAD_MAX_BARRIER_SIZE);
>  	pfdev->features.coherency_features = gpu_read(pfdev, GPU_COHERENCY_FEATURES);
> +	pfdev->features.afbc_features = gpu_read(pfdev, GPU_AFBC_FEATURES);
>  	for (i = 0; i < 4; i++)
>  		pfdev->features.texture_features[i] = gpu_read(pfdev, GPU_TEXTURE_FEATURES(i));
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_regs.h b/drivers/gpu/drm/panfrost/panfrost_regs.h
> index eddaa62ad..dc9df5457 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_regs.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_regs.h
> @@ -82,6 +82,7 @@
>  
>  #define GPU_TEXTURE_FEATURES(n)		(0x0B0 + ((n) * 4))
>  #define GPU_JS_FEATURES(n)		(0x0C0 + ((n) * 4))
> +#define GPU_AFBC_FEATURES		(0x4C)	/* (RO) AFBC support on Bifrost */
>  
>  #define GPU_SHADER_PRESENT_LO		0x100	/* (RO) Shader core present bitmap, low word */
>  #define GPU_SHADER_PRESENT_HI		0x104	/* (RO) Shader core present bitmap, high word */
> diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h
> index ec19db1ee..061e700dd 100644
> --- a/include/uapi/drm/panfrost_drm.h
> +++ b/include/uapi/drm/panfrost_drm.h
> @@ -171,6 +171,7 @@ enum drm_panfrost_param {
>  	DRM_PANFROST_PARAM_JS_FEATURES15,
>  	DRM_PANFROST_PARAM_NR_CORE_GROUPS,
>  	DRM_PANFROST_PARAM_THREAD_TLS_ALLOC,
> +	DRM_PANFROST_PARAM_AFBC_FEATURES,
>  };
>  
>  struct drm_panfrost_get_param {
>