linux-kernel - Re: [RFC PATCH] drm/panfrost: Handle IDVS_GROUP

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Date:   Sun, 9 Jan 2022 12:20:03 -0500
From:   Alyssa Rosenzweig <alyssa@...labora.com>
To:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Cc:     dri-devel@...ts.freedesktop.org, Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Steven Price <steven.price@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] drm/panfrost: Handle IDVS_GROUP_SIZE feature

kbase dt-bindings say that tasks are sent to cores in groups of N + 1,
where N is the value here. So our old behaviour sends tasks in groups of
1; the new behaviour sends tasks in groups of 16. I assume this has
performance implications but no conformance implications.

Searching GitHub, I can't find any device trees that set
idvs-group-size out of the many random Android forks people have
uploaded, so I don't think this will matter for any production device.
(Was this a workaround for preproduction silicon? or FPGAs? or was this
an option for the sake of having an option?)

On Sun, Jan 09, 2022 at 12:12:54PM -0500, Alyssa Rosenzweig wrote:
> The IDVS group size feature was missing. It is used on some Bifrost and
> Valhall GPUs, and is the last kernel-relevant Bifrost feature we're
> missing.
> 
> This feature adds an extra IDVS group size field to the JM_CONFIG
> register. In kbase, the value is configurable via the device tree; kbase
> uses 0xF as a default if no value is specified. Until we find a device
> demanding otherwise, let's always set the 0xF default on devices which
> support this feature mimicking kbase's behaviour.
> 
> As JM_CONFIG is an undocumented register, it's not clear to me what
> happens if we fail to include this handling. Index-driven vertex shading
> already works on Bifrost boards with this feature without this handling.
> Perhaps this has performance implications? Patch untested for the
> moment, wanted to give Steven a chance to comment.
> 
> Applies on top of my feature clean up series which should go in first.
> (That's pure cleaunp, this is a behaviour change RFC needing
> discussion.)
> 
> Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_features.h | 3 +++
>  drivers/gpu/drm/panfrost/panfrost_gpu.c      | 3 +++
>  drivers/gpu/drm/panfrost/panfrost_regs.h     | 1 +
>  3 files changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_features.h b/drivers/gpu/drm/panfrost/panfrost_features.h
> index 34f2bae1ec8c..36fadcf9634e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_features.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_features.h
> @@ -20,6 +20,7 @@ enum panfrost_hw_feature {
>  	HW_FEATURE_AARCH64_MMU,
>  	HW_FEATURE_TLS_HASHING,
>  	HW_FEATURE_THREAD_GROUP_SPLIT,
> +	HW_FEATURE_IDVS_GROUP_SIZE,
>  	HW_FEATURE_3BIT_EXT_RW_L2_MMU_CONFIG,
>  };
>  
> @@ -74,6 +75,7 @@ enum panfrost_hw_feature {
>  	BIT_ULL(HW_FEATURE_FLUSH_REDUCTION) | \
>  	BIT_ULL(HW_FEATURE_PROTECTED_MODE) | \
>  	BIT_ULL(HW_FEATURE_PROTECTED_DEBUG_MODE) | \
> +	BIT_ULL(HW_FEATURE_IDVS_GROUP_SIZE) | \
>  	BIT_ULL(HW_FEATURE_COHERENCY_REG))
>  
>  #define hw_features_g76 (\
> @@ -87,6 +89,7 @@ enum panfrost_hw_feature {
>  	BIT_ULL(HW_FEATURE_COHERENCY_REG) | \
>  	BIT_ULL(HW_FEATURE_AARCH64_MMU) | \
>  	BIT_ULL(HW_FEATURE_TLS_HASHING) | \
> +	BIT_ULL(HW_FEATURE_IDVS_GROUP_SIZE) | \
>  	BIT_ULL(HW_FEATURE_3BIT_EXT_RW_L2_MMU_CONFIG))
>  
>  #define hw_features_g31 (\
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index bbe628b306ee..50c8922694d7 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -145,6 +145,9 @@ static void panfrost_gpu_init_quirks(struct panfrost_device *pfdev)
>  		quirks |= (COHERENCY_ACE_LITE | COHERENCY_ACE) <<
>  			   JM_FORCE_COHERENCY_FEATURES_SHIFT;
>  
> +	if (panfrost_has_hw_feature(pfdev, HW_FEATURE_IDVS_GROUP_SIZE))
> +		quirks |= JM_DEFAULT_IDVS_GROUP_SIZE << JM_IDVS_GROUP_SIZE_SHIFT;
> +
>  	if (quirks)
>  		gpu_write(pfdev, GPU_JM_CONFIG, quirks);
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_regs.h b/drivers/gpu/drm/panfrost/panfrost_regs.h
> index 6c5a11ef1ee8..16e776cc82ea 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_regs.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_regs.h
> @@ -208,6 +208,7 @@
>  #define JM_MAX_JOB_THROTTLE_LIMIT	0x3F
>  #define JM_FORCE_COHERENCY_FEATURES_SHIFT 2
>  #define JM_IDVS_GROUP_SIZE_SHIFT	16
> +#define JM_DEFAULT_IDVS_GROUP_SIZE	0xF
>  #define JM_MAX_IDVS_GROUP_SIZE		0x3F
>  
>  
> -- 
> 2.34.1
>