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Date:   Thu, 18 Jan 2018 14:45:48 +0100
From:   Boris Brezillon <boris.brezillon@free-electrons.com>
To:     Eric Anholt <eric@anholt.net>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/vc4: Flush the caches before the bin jobs, as well.
Message-ID: <20180118144548.3db88ecf@bbrezillon>
In-Reply-To: <20171221221722.23809-1-eric@anholt.net>
References: <20171221221722.23809-1-eric@anholt.net>
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On Thu, 21 Dec 2017 14:17:22 -0800
Eric Anholt <eric@anholt.net> wrote:

> If the frame samples from a render target that was just written, its
> cache flush during the binning step may have occurred before the
> previous frame's RCL was completed.  Flush the texture caches again
> before starting each RCL job to make sure that the sampling of the
> previous RCL's output is correct.
> 
> Fixes flickering in the top left of 3DMMES Taiji.
> 
> Signed-off-by: Eric Anholt <eric@anholt.net>
> Fixes: ca26d28bbaa3 ("drm/vc4: improve throughput by pipelining binning and rendering jobs")

Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>

> ---
>  drivers/gpu/drm/vc4/vc4_gem.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
> index 6c32c89a83a9..afa7fe21b35e 100644
> --- a/drivers/gpu/drm/vc4/vc4_gem.c
> +++ b/drivers/gpu/drm/vc4/vc4_gem.c
> @@ -436,6 +436,19 @@ vc4_flush_caches(struct drm_device *dev)
>  		  VC4_SET_FIELD(0xf, V3D_SLCACTL_ICC));
>  }
>  
> +static void
> +vc4_flush_texture_caches(struct drm_device *dev)
> +{
> +	struct vc4_dev *vc4 = to_vc4_dev(dev);
> +
> +	V3D_WRITE(V3D_L2CACTL,
> +		  V3D_L2CACTL_L2CCLR);
> +
> +	V3D_WRITE(V3D_SLCACTL,
> +		  VC4_SET_FIELD(0xf, V3D_SLCACTL_T1CC) |
> +		  VC4_SET_FIELD(0xf, V3D_SLCACTL_T0CC));
> +}
> +
>  /* Sets the registers for the next job to be actually be executed in
>   * the hardware.
>   *
> @@ -474,6 +487,14 @@ vc4_submit_next_render_job(struct drm_device *dev)
>  	if (!exec)
>  		return;
>  
> +	/* A previous RCL may have written to one of our textures, and
> +	 * our full cache flush at bin time may have occurred before
> +	 * that RCL completed.  Flush the texture cache now, but not
> +	 * the instructions or uniforms (since we don't write those
> +	 * from an RCL).
> +	 */
> +	vc4_flush_texture_caches(dev);
> +
>  	submit_cl(dev, 1, exec->ct1ca, exec->ct1ea);
>  }
>