linux-kernel - Re: [PATCH] lib/genalloc.c: add check gen_pool_dma

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Date:	Fri, 24 Jan 2014 08:40:28 +0530
From:	Sachin Kamat <sachin.kamat@...aro.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Prabhakar Lad <prabhakar.csengg@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Nicolin Chen <b42378@...escale.com>,
	Joe Perches <joe@...ches.com>,
	LKML <linux-kernel@...r.kernel.org>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>
Subject: Re: [PATCH] lib/genalloc.c: add check gen_pool_dma_alloc() if dma
 pointer is not NULL

On 24 January 2014 02:53, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Thu, 23 Jan 2014 15:51:31 +0530 Prabhakar Lad <prabhakar.csengg@...il.com> wrote:
>
>> Hi Sachin,
>>
>> On Thu, Jan 23, 2014 at 3:38 PM, Sachin Kamat <sachin.kamat@...aro.org> wrote:
>> > Hi Prabhakar,
>> >
>> > On 23 January 2014 15:26, Prabhakar Lad <prabhakar.csengg@...il.com> wrote:
>> >> From: "Lad, Prabhakar" <prabhakar.csengg@...il.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@...il.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.

Makes sense. Thanks Andrew.

-- 
With warm regards,
Sachin
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