Re: [PATCH 2/2] media: bt8xx: avoid a useless memset

[Joe Perches]

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;
 }