Re: [PATCH] lib/genalloc.c: add check gen_pool_dma_alloc() if dma pointer is not NULL

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 23 Jan 2014 15:51:31 +0530 Prabhakar Lad <prabhakar.csengg@gmail.com> wrote:

> Hi Sachin,
> 
> On Thu, Jan 23, 2014 at 3:38 PM, Sachin Kamat <sachin.kamat@linaro.org> wrote:
> > Hi Prabhakar,
> >
> > On 23 January 2014 15:26, Prabhakar Lad <prabhakar.csengg@gmail.com> wrote:
> >> From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
> >>
> >> In the gen_pool_dma_alloc() the dma pointer can be NULL
> >> and while assigning gen_pool_virt_to_phys(pool, vaddr) to
> >> dma caused the following crash on da850 evm,
> >>
> > [snip]
> >>
> >> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
> >> ---
> >>  lib/genalloc.c |    3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/lib/genalloc.c b/lib/genalloc.c
> >> index dda3116..f48163f 100644
> >> --- a/lib/genalloc.c
> >> +++ b/lib/genalloc.c
> >> @@ -334,7 +334,8 @@ void *gen_pool_dma_alloc(struct gen_pool *pool, size_t size, dma_addr_t *dma)
> >>         if (!vaddr)
> >>                 return NULL;
> >>
> >> -       *dma = gen_pool_virt_to_phys(pool, vaddr);
> >> +       if (dma)
> >> +               *dma = gen_pool_virt_to_phys(pool, vaddr);
> >
> > Wouldn't it be better to return (with error/message) if dma is NULL
> > rather than silently ignore it?
> >
> I am not sure if returning here with error is OK,
> may be just adding a warning message could be OK ?

The patch look OK as-is to me.  `dma' is a second return value from
gen_pool_dma_alloc() and this patch extends the gen_pool_dma_alloc()
interface by making that return value optional.  That's good for
callers who don't want the physical address, and they can call
gen_pool_virt_to_phys() at a later time to get the physical address
anyway.

>From my reading, 3.13.x kernels will need this patch.

I suppose we should document the API change:

--- a/lib/genalloc.c~lib-genallocc-add-check-gen_pool_dma_alloc-if-dma-pointer-is-not-null-fix
+++ a/lib/genalloc.c
@@ -316,7 +316,7 @@ EXPORT_SYMBOL(gen_pool_alloc);
  * gen_pool_dma_alloc - allocate special memory from the pool for DMA usage
  * @pool: pool to allocate from
  * @size: number of bytes to allocate from the pool
- * @dma: dma-view physical address
+ * @dma: dma-view physical address return value.  Use NULL if unneeded.
  *
  * Allocate the requested number of bytes from the specified pool.
  * Uses the pool allocation function (with first-fit algorithm by default).
_