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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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@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.

> Yes, I think that's more understandable.
>
> > By the way, shifting left by fmt should be fine for TILFMT_8BIT,
> > TILFMT_16BIT and TILFMT_32BIT that evaluate to 0, 1 and 2 respectively,
> > but how does it work with TILFMT_PAGE ? fmt is computed by gem2fmt() in
> > call cases, which returns TILFMT_PAGE in the default case (no tiled flag
> > set). Can this happen in practice ?
> 
> These functions are only called for 2D buffers. I do find shifting by
> 'enum tiler_fmt' quite ugly, though...

So do I. This should be added to the infinite todo list :-)

-- 
Regards,

Laurent Pinchart

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