[PATCH] drm/omap: fix tiled buffer stride calculations

[Tomi Valkeinen]

On 18/05/17 14:25, Laurent Pinchart wrote:
> Hi Tomi,
> 
> On Thursday 18 May 2017 14:14:35 Tomi Valkeinen wrote:
>> On 18/05/17 13:59, Laurent Pinchart wrote:
>>> On Thursday 18 May 2017 13:28:26 Tomi Valkeinen wrote:
>>>> omap_gem uses page alignment for buffer stride. The related calculations
>>>> are a bit off, though, as byte stride of 4096 gets aligned to 8192,
>>>> instead of 4096. This patch fixes those calculations.
>>>>
>>>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
>>>> ---
>>>>
>>>>  drivers/gpu/drm/omapdrm/omap_gem.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c
>>>> b/drivers/gpu/drm/omapdrm/omap_gem.c index 13abf221d153..4c41000ff4c4
>>>> 100644
>>>> --- a/drivers/gpu/drm/omapdrm/omap_gem.c
>>>> +++ b/drivers/gpu/drm/omapdrm/omap_gem.c
>>>> @@ -182,7 +182,7 @@ static void evict_entry(struct drm_gem_object *obj,
>>>>  	size_t size = PAGE_SIZE * n;
>>>>  	loff_t off = mmap_offset(obj) +
>>>>  			(entry->obj_pgoff << PAGE_SHIFT);
>>>> -	const int m = 1 + ((omap_obj->width << fmt) / PAGE_SIZE);
>>>> +	const int m = 1 + (((omap_obj->width - 1) << fmt) / PAGE_SIZE);
>>>
>>> How about
>>>
>>> 	int m = round_up(omap_obj->width << fmt, PAGE_SIZE);
>>>
>>> instead of open-coding it ? I find that a bit easier to understand.
>>
>> That should be:
>>
>> round_up(omap_obj->width << fmt, PAGE_SIZE) / PAGE_SIZE;
> 
> Sorry, I meant DIV_ROUND_UP, not round_up.

Ah, of course. Not my day... =)

From: Tomi Valkeinen <tomi.valkeinen at ti.com>
Date: Thu, 18 May 2017 11:51:51 +0300
Subject: [PATCH] drm/omap: fix tiled buffer stride calculations

omap_gem uses page alignment for buffer stride. The related calculations
are a bit off, though, as byte stride of 4096 gets aligned to 8192,
instead of 4096.

This patch changes the code to use DIV_ROUND_UP(), which fixes those
calculations and makes them more readable.

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

diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index 13abf221d153..5c5c86ddd6f4 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -182,7 +182,7 @@ static void evict_entry(struct drm_gem_object *obj,
 	size_t size = PAGE_SIZE * n;
 	loff_t off = mmap_offset(obj) +
 			(entry->obj_pgoff << PAGE_SHIFT);
-	const int m = 1 + ((omap_obj->width << fmt) / PAGE_SIZE);
+	const int m = DIV_ROUND_UP(omap_obj->width << fmt, PAGE_SIZE);
 
 	if (m > 1) {
 		int i;
@@ -424,7 +424,7 @@ static int fault_2d(struct drm_gem_object *obj,
 	 * into account in some of the math, so figure out virtual stride
 	 * in pages
 	 */
-	const int m = 1 + ((omap_obj->width << fmt) / PAGE_SIZE);
+	const int m = DIV_ROUND_UP(omap_obj->width << fmt, PAGE_SIZE);
 
 	/* We don't use vmf->pgoff since that has the fake offset: */
 	pgoff = (vmf->address - vma->vm_start) >> PAGE_SHIFT;

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