Re: [PATCH 3/4] drm/omap: remove align_pitch()

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

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On 19/04/16 05:12, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Monday 18 Apr 2016 18:42:13 Tomi Valkeinen wrote:
>> The previous commit removed aligning the pitch to SGX's pitch
>> requirement from align_pitch(). What's left is effectively a function
>> that returns width * bytespp.
>>
>> To clean up the driver, we can remove the function and have the
>> calculation inline in the two places which call align_pitch().
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> I wonder, however, if the calculation is correct. Shouldn't the pitch be 
> calculated as DIV_ROUND_UP(width * bpp, 8) instead of width * 
> DIV_ROUND_UP(bpp, 8) ?

Well, in practice it doesn't matter. The bpps we use, 32/24/16 are all
divisible by 8. So I don't really even know why the div round up is there in
the first place.

There's the 12 bit RGB, in a 16 bit container, which in theory works but I
don't think we have ever used it or really supported it. If 'bpp' is 12 in this
case, width * DIV_ROUND_UP(bpp, 8) gives the correct pitch. But then, I guess
'bpp' should be 16 in this case, as the omap_gem.c part is about allocating
memory, without knowing the format.

Then there are the 1/2/4/8 bpp CLUT modes, which we have never supported (and
they are no longer supported by the HW in recent HW). For those,
DIV_ROUND_UP(width * bpp, 8) would be correct.

So... I think you are right. Here:

From c435ebfc5953d4983c5772ec4fb7c5b0d01ecb9f Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <tomi.valkeinen@ti.com>
Date: Tue, 19 Apr 2016 09:06:32 +0300
Subject: [PATCH] drm/omap: fix pitch round-up

At the moment we calculate the buffer's pitch with:

  pitch = width * DIV_ROUND_UP(bpp, 8)

For CLUT modes with bpp of 1/2/4/8 this gives wrong result, and the
correct pitch is:

  pitch = DIV_ROUND_UP(width * bpp, 8)

In practice this doesn't change anything, as we don't support CLUT
modes, but it's better to have the pitch calculation correct.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
index cb6af7757720..42831b8c46b9 100644
--- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
+++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
@@ -125,8 +125,8 @@ static int omap_fbdev_create(struct drm_fb_helper *helper,
 	mode_cmd.width = sizes->surface_width;
 	mode_cmd.height = sizes->surface_height;
 
-	mode_cmd.pitches[0] = mode_cmd.width *
-		DIV_ROUND_UP(sizes->surface_bpp, 8);
+	mode_cmd.pitches[0] =
+			DIV_ROUND_UP(mode_cmd.width * sizes->surface_bpp, 8);
 
 	fbdev->ywrap_enabled = priv->has_dmm && ywrap_enabled;
 	if (fbdev->ywrap_enabled) {
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index 7ea1e00d8ca6..23af01eb1773 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -660,7 +660,7 @@ int omap_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
 {
 	union omap_gem_size gsize;
 
-	args->pitch = args->width * DIV_ROUND_UP(args->bpp, 8);
+	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
 
 	args->size = PAGE_ALIGN(args->pitch * args->height);
 


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