2014-07-28 11:21:01

by Pavel Machek

Subject: [PATCH] work around warning in i915_gem_gtt

Gcc warns that addr might be used uninitialized. It may not, but I see
why gcc gets confused.

Additionally, hiding code with side-effects inside WARN_ON() argument
seems uncool, so I moved it outside.

Signed-off-by: Pavel Machek <[email protected]>

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 8b3cde7..8fcc974 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1448,7 +1448,7 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
(gen6_gtt_pte_t __iomem *)dev_priv->gtt.gsm + first_entry;
int i = 0;
struct sg_page_iter sg_iter;
- dma_addr_t addr;
+ dma_addr_t addr = 0;

for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
addr = sg_page_iter_dma_address(&sg_iter);
@@ -1462,9 +1462,10 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
* of NUMA access patterns. Therefore, even with the way we assume
* hardware should work, we must keep this posting read for paranoia.
*/
- if (i != 0)
- WARN_ON(readl(&gtt_entries[i-1]) !=
- vm->pte_encode(addr, level, true));
+ if (i != 0) {
+ unsigned long gtt = readl(&gtt_entries[i-1]);
+ WARN_ON(gtt != vm->pte_encode(addr, level, true));
+ }

/* This next bit makes the above posting read even more important. We
* want to flush the TLBs only after we're certain all the PTE updates

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

2014-07-28 15:24:44

by Daniel Vetter

Subject: Re: [PATCH] work around warning in i915_gem_gtt

On Mon, Jul 28, 2014 at 01:20:58PM +0200, Pavel Machek wrote:
>
> Gcc warns that addr might be used uninitialized. It may not, but I see
> why gcc gets confused.
>
> Additionally, hiding code with side-effects inside WARN_ON() argument
> seems uncool, so I moved it outside.
>
> Signed-off-by: Pavel Machek <[email protected]>
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 8b3cde7..8fcc974 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -1448,7 +1448,7 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
> (gen6_gtt_pte_t __iomem *)dev_priv->gtt.gsm + first_entry;
> int i = 0;
> struct sg_page_iter sg_iter;
> - dma_addr_t addr;
> + dma_addr_t addr = 0;

I want to have a /* shuts up gcc */ for these kinds of things, where we
need to help out the compiler. Added and merged, thanks.
-Daniel

>
> for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
> addr = sg_page_iter_dma_address(&sg_iter);
> @@ -1462,9 +1462,10 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
> * of NUMA access patterns. Therefore, even with the way we assume
> * hardware should work, we must keep this posting read for paranoia.
> */
> - if (i != 0)
> - WARN_ON(readl(&gtt_entries[i-1]) !=
> - vm->pte_encode(addr, level, true));
> + if (i != 0) {
> + unsigned long gtt = readl(&gtt_entries[i-1]);
> + WARN_ON(gtt != vm->pte_encode(addr, level, true));
> + }
>
> /* This next bit makes the above posting read even more important. We
> * want to flush the TLBs only after we're certain all the PTE updates
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
> _______________________________________________
> dri-devel mailing list
> [email protected]
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch