Re: [PATCH 09/21] drm/omap: handle mismatching color format and buffer width

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 02/03/15 12:22, Daniel Stone wrote:

>> I don't know why Rob named it like that. "The bpp of the stride"? Shrug.
> 
> It's just the bpp of the pixel format; it's not at all associated with
> the stride?

The comment says "this times width is stride", so I thought the naming comes
from that train of thought. But I agree, it's just bpp.

Here's updated patch:

From af0db526ae274d47488ec49577365909eb8f629d Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <tomi.valkeinen@ti.com>
Date: Thu, 25 Sep 2014 19:24:28 +0000
Subject: [PATCH] drm/omap: handle incompatible buffer stride and pixel size

omapdrm doesn't check if the pitch of the framebuffer and the color
format's bits-per-pixel are compatible. omapdss requires that the stride
of a buffer is an integer number of pixels

For example, when using modetest with a display that has x resolution of
1280, and using packed 24 RGB mode (3 bytes per pixel), modetest
allocates a buffer with a byte stride of 4 * 1280 = 5120. But 5120 / 3 =
1706.666... pixels, which causes wrong colors and a tilt on the screen.

Add a check into omapdrm to return an error if the user tries to use
such a combination.

Note: this is not a HW requirement at least for non-rotation use cases,
but a SW driver requirement. In the future we should study if also
rotation use cases are fine with any stride size, and if so, change the
driver to allow these strides.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
---
 drivers/gpu/drm/omapdrm/omap_fb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/omapdrm/omap_fb.c b/drivers/gpu/drm/omapdrm/omap_fb.c
index 2975096abdf5..e123b4dee670 100644
--- a/drivers/gpu/drm/omapdrm/omap_fb.c
+++ b/drivers/gpu/drm/omapdrm/omap_fb.c
@@ -463,6 +463,14 @@ struct drm_framebuffer *omap_framebuffer_init(struct drm_device *dev,
 			goto fail;
 		}
 
+		if (pitch % format->planes[i].stride_bpp != 0) {
+			dev_err(dev->dev,
+				"buffer pitch (%d bytes) is not a multiple of pixel size (%d bytes)\n",
+				pitch, format->planes[i].stride_bpp);
+			ret = -EINVAL;
+			goto fail;
+		}
+
 		size = pitch * mode_cmd->height / format->planes[i].sub_y;
 
 		if (size > (omap_gem_mmap_size(bos[i]) - mode_cmd->offsets[i])) {
-- 
2.3.1




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