[RFC] etnaviv: flush color cache and depth cache together before resolves

[Wladimir J. van der Laan]

On Tue, May 30, 2017 at 12:50:07PM +0200, Philipp Zabel wrote:
> Before resolving a rendertarget or a depth/stencil resource into a
> texture, flush both the color cache and the depth cache together.
> 
> It is unclear whether this is necessary for the following stall to
> work properly, or whether the depth flush just adds enough time
> for the color cache flush to finish before the resolver is started,
> but this change removes artifacts that otherwise appear if a texture
> is sampled directly after rendering into it.
> 
> The test case is a simple QML scene graph with a QtWebEngine based
> WebView rendered on top of a blue background:
> 
> 	import QtQuick 2.0
> 	import QtQuick.Window 2.2
> 	import QtWebView 1.1
> 
> 	Window {
> 		Rectangle {
> 			id: background
> 			anchors.fill: parent
> 			color: "blue"
> 		}
> 
> 		WebView {
> 			id: webView
> 			anchors.fill: parent
> 		}
> 
> 		Component.onCompleted: {
> 			webView.url = "<some animated website>"
> 		}
> 	}
> 
> If the website is animated, the WebView renders the site contents into
> texture tiles and immediately afterwards samples from them to draw the
> tiles into the Qt renderbuffer. Without this patch, a small irregular
> triangle in the lower right of each browser tile appears solid blue, as
> if the texture sampler samples zeroes instead of the website contents,
> and the previously rendered blue Rectangle shows through.
> 
> Other attempts such as adding a pipeline stall before the color flush or
> a TS cache flush afterwards or flushing multiple times, with stalls
> before and after each flush, have shown no effect.
> 
> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> ---
>  src/gallium/drivers/etnaviv/etnaviv_clear_blit.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c b/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> index ae1c586288..faa6bd0436 100644
> --- a/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> +++ b/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> @@ -455,15 +455,10 @@ etna_try_rs_blit(struct pipe_context *pctx,
>        ts_mem_config |= VIVS_TS_MEM_CONFIG_MSAA | msaa_format;
>     }
>  
> -   uint32_t to_flush = 0;
> -
> -   if (src->base.bind & PIPE_BIND_RENDER_TARGET)
> -      to_flush |= VIVS_GL_FLUSH_CACHE_COLOR;
> -   if (src->base.bind & PIPE_BIND_DEPTH_STENCIL)
> -      to_flush |= VIVS_GL_FLUSH_CACHE_DEPTH;
> -
> -   if (to_flush) {
> -      etna_set_state(ctx->stream, VIVS_GL_FLUSH_CACHE, to_flush);
> +   if (src->base.bind & PIPE_BIND_RENDER_TARGET ||
> +       src->base.bind & PIPE_BIND_DEPTH_STENCIL) {
> +      etna_set_state(ctx->stream, VIVS_GL_FLUSH_CACHE,
> +		     VIVS_GL_FLUSH_CACHE_COLOR | VIVS_GL_FLUSH_CACHE_DEPTH);

Can you please add a comment here, describing (as above) why both
caches are flushed?

These things are hard to get right, so any bit of documentation why
a certain choice was made while reading the code helps.

>        etna_stall(ctx->stream, SYNC_RECIPIENT_RA, SYNC_RECIPIENT_PE);
>     }
>  
> -- 
> 2.11.0
> 
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