linux-kernel - [PATCH] drm: Use horizontal and vertical chroma subsampling factor while calculating offsets in the physical address of framebuffer

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Message-Id: <1534527184-24552-1-git-send-email-ayan.halder@arm.com>
Date:   Fri, 17 Aug 2018 18:33:04 +0100
From:   Ayan Kumar Halder <ayan.halder@....com>
To:     ayan.halder@....com, liviu.dudau@....com, brian.starkey@....com,
        gustavo@...ovan.org, maarten.lankhorst@...ux.intel.com,
        seanpaul@...omium.org, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     nd@....com
Subject: [PATCH] drm: Use horizontal and vertical chroma subsampling factor while calculating offsets in the physical address of framebuffer

For multi-planar formats, while calculating offsets in planes with index greater than 0
(ie second plane, third plane, etc), one needs to divide (src_x * cpp) with horizontal
chroma subsampling factor and (src_y * pitch) with vertical chroma subsampling factor.

The reason being that the planes contain subsampled (ie reduced) data (by a factor of 2) and thus the
while calculating the byte position coresponding to the x and y co-ordinates, one needs to be
divide it with the sampling factor.

Signed-off-by: Ayan Kumar halder <ayan.halder@....com>
---
 drivers/gpu/drm/drm_fb_cma_helper.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index b127061..47e0e2f 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -86,14 +86,21 @@ dma_addr_t drm_fb_cma_get_gem_addr(struct drm_framebuffer *fb,
 {
 	struct drm_gem_cma_object *obj;
 	dma_addr_t paddr;
+	u8 h_div = 1, v_div = 1;
 
 	obj = drm_fb_cma_get_gem_obj(fb, plane);
 	if (!obj)
 		return 0;
 
 	paddr = obj->paddr + fb->offsets[plane];
-	paddr += fb->format->cpp[plane] * (state->src_x >> 16);
-	paddr += fb->pitches[plane] * (state->src_y >> 16);
+
+	if (plane > 0) {
+		h_div = fb->format->hsub;
+		v_div = fb->format->vsub;
+	}
+
+	paddr += (fb->format->cpp[plane] * (state->src_x >> 16)) / h_div;
+	paddr += (fb->pitches[plane] * (state->src_y >> 16)) / v_div;
 
 	return paddr;
 }
-- 
2.7.4