[PATCH 3/8] drm/rockchip: vop2: Don't accept AFBC YTR for RGB565 on RK3588

[Arun Iyengar via B4 Relay <devnull+aiyengar1990.gmail.com@kernel.org>]

From: Arun Iyengar <aiyengar1990@gmail.com>

The Cluster windows of the RK3588 VOP2 advertise every AFBC modifier
of format_modifiers_afbc for RGB565 and BGR565, including the ones
with the lossless colour transform (YTR). Scanning out an RGB565
buffer rendered by the Mali-G610 (panfrost) with
AFBC(16x16 | SPARSE | YTR) gives a black picture and POST_BUF_EMPTY
on the video port, on every Cluster window, while the same buffer
rendered with AFBC(16x16 | SPARSE) displays correctly, as do 32 bpp
formats with YTR.

YTR on RGB565 is also a questionable pairing to start with:
Documentation/gpu/afbc.rst requires the R, G, B component order when
YTR is used, with component 0 in the least significant bits, which
DRM_FORMAT_RGB565 (B in the low bits) doesn't have, and the Arm
Mali-D71 (komeda) only accepts AFBC for BGR565.

Stop advertising and accepting YTR for the two 16 bpp RGB formats on
RK3588, so that userspace picks a modifier the decoder handles. The
BGR565 case could not be tested (Mesa can't import BGR565 dma-bufs),
it's rejected as well because the decoder is configured identically
for both formats, apart from the R/B swap after decoding.

Fixes: 5a028e8f062f ("drm/rockchip: vop2: Add support for rk3588")
Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
---
 drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
index 76d151b8bc52..629ea7f11250 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
@@ -404,6 +404,18 @@ static bool rockchip_vop2_mod_supported(struct drm_plane *plane, u32 format,
 	if (vop2_convert_afbc_format(format) == VOP2_AFBC_FMT_INVALID)
 		return false;
 
+	/*
+	 * The AFBC decoder of the RK3588 Cluster windows can't decode 16 bpp
+	 * RGB that uses the lossless colour transform: the picture stays
+	 * black and the video port reports POST_BUF_EMPTY, while the same
+	 * buffers without YTR display fine.
+	 */
+	if (vop2->version == VOP_VERSION_RK3588 && (modifier & AFBC_FORMAT_MOD_YTR) &&
+	    (format == DRM_FORMAT_RGB565 || format == DRM_FORMAT_BGR565)) {
+		drm_dbg_kms(vop2->drm, "No AFBC YTR support for 16 bpp RGB\n");
+		return false;
+	}
+
 	/* Different windows have different format/modifier support */
 	for (i = 0; i < plane->modifier_count; i++) {
 		if (plane->modifiers[i] == modifier)

-- 
2.55.0