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SubjectRe: [PATCH 2/2] media: bt8xx: avoid a useless memset
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Le 27/07/2020 à 18:16, Joe Perches a écrit :
> On Mon, 2020-07-27 at 09:09 -0700, Joe Perches wrote:
>> On Mon, 2020-07-27 at 15:51 +0200, Christophe JAILLET wrote:
>>> Avoid a memset after a call to 'dma_alloc_coherent()'.
>>> This is useless since
>>> commit 518a2f1925c3 ("dma-mapping: zero memory returned from dma_alloc_*")
>> []
>>> diff --git a/drivers/media/pci/bt8xx/btcx-risc.c b/drivers/media/pci/bt8xx/btcx-risc.c
>> []
>>> @@ -73,7 +73,6 @@ int btcx_riscmem_alloc(struct pci_dev *pci,
>>> dprintk("btcx: riscmem alloc [%d] dma=%lx cpu=%p size=%d\n",
>>> memcnt, (unsigned long)dma, cpu, size);
>>> }
>>> - memset(risc->cpu,0,risc->size);
>>> return 0;
>>> }
>>
>> Likely NAK.
>>
>> This is not useless as risc->cpu may be reused
>> and the alloc may not have been done.
>
> Perhaps a little rewrite for clarity:
> ---
> drivers/media/pci/bt8xx/btcx-risc.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/media/pci/bt8xx/btcx-risc.c b/drivers/media/pci/bt8xx/btcx-risc.c
> index 51257980f539..311f4ca2a108 100644
> --- a/drivers/media/pci/bt8xx/btcx-risc.c
> +++ b/drivers/media/pci/bt8xx/btcx-risc.c
> @@ -56,24 +56,26 @@ int btcx_riscmem_alloc(struct pci_dev *pci,
> struct btcx_riscmem *risc,
> unsigned int size)
> {
> - __le32 *cpu;
> - dma_addr_t dma = 0;
> -
> - if (NULL != risc->cpu && risc->size < size)
> - btcx_riscmem_free(pci,risc);
> - if (NULL == risc->cpu) {
> - cpu = pci_alloc_consistent(pci, size, &dma);
> - if (NULL == cpu)
> + if (risc->cpu && risc->size < size)
> + btcx_riscmem_free(pci, risc);
> +
> + if (risc->cpu) {
> + memset(risc->cpu, 0, risc->size);
> + } else {
> + dma_addr_t dma = 0;
> +
> + risc->cpu = pci_alloc_consistent(pci, size, &dma);
> + if (!risc->cpu)
> return -ENOMEM;
> - risc->cpu = cpu;
> +
> risc->dma = dma;
> risc->size = size;
>
> memcnt++;
> dprintk("btcx: riscmem alloc [%d] dma=%lx cpu=%p size=%d\n",
> - memcnt, (unsigned long)dma, cpu, size);
> + memcnt, (unsigned long)dma, risc->cpu, size);
> }
> - memset(risc->cpu,0,risc->size);
> +
> return 0;
> }
>
>
>
Looks good to me.

Just note, that this will not apply after patch 1/2 is applied, because
it turns pci_alloc_consistent() into dma_alloc_coherent().

CJ

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