linux-kernel - Re: [PATCH] arch/powerpc: Use dma_zalloc

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Date:   Thu, 15 Nov 2018 11:25:07 -0800
From:   Joe Perches <joe@...ches.com>
To:     Sabyasachi Gupta <sabyasachi.linux@...il.com>,
        benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        darren@...vens-zone.net, christophe.leroy@....fr,
        geoff@...radead.org
Cc:     Souptick Joarder <jrdr.linux@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch/powerpc: Use dma_zalloc_coherent

On Thu, 2018-11-15 at 23:29 +0530, Sabyasachi Gupta wrote:
> On Mon, Nov 5, 2018 at 8:58 AM Sabyasachi Gupta
> <sabyasachi.linux@...il.com> wrote:
> > Replaced dma_alloc_coherent + memset with dma_zalloc_coherent
> > 
> > Signed-off-by: Sabyasachi Gupta <sabyasachi.linux@...il.com>
> 
> Any comment on this patch?

It's obviously correct.

You might realign the arguments on the next lines
to the open parenthesis.

Perhaps there should be new function calls
added for symmetry to the other alloc functions
for multiplication overflow protection.

Perhaps:

void *dma_alloc_array_coherent()
void *dma_calloc_coherent()

Something like
---
 include/linux/dma-mapping.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 15bd41447025..95bebf8883b1 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -565,6 +565,25 @@ static inline void *dma_alloc_coherent(struct device *dev, size_t size,
 			(gfp & __GFP_NOWARN) ? DMA_ATTR_NO_WARN : 0);
 }
 
+static inline void *dma_alloc_array_coherent(struct device *dev,
+					     size_t n, size_t size,
+					     dma_addr_t *dma_handle, gfp_t gfp)
+{
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(n, size, &bytes)))
+		return NULL;
+	return dma_alloc_coherent(dev, bytes, dma_handle, gfp);
+}
+
+static inline void *dma_calloc_coherent(struct device *dev,
+					size_t n, size_t size,
+					dma_addr_t *dma_handle, gfp_t gfp)
+{
+	return dma_alloc_array_coherent(dev, n, size, dma_handle,
+					gfp | __GFP_ZERO);
+}
+
 static inline void dma_free_coherent(struct device *dev, size_t size,
 		void *cpu_addr, dma_addr_t dma_handle)
 {

---
> > diff --git a/arch/powerpc/platforms/pasemi/dma_lib.c b/arch/powerpc/platforms/pasemi/dma_lib.c
[]
> > @@ -255,15 +255,13 @@ int pasemi_dma_alloc_ring(struct pasemi_dmachan *chan, int ring_size)
> > 
> >         chan->ring_size = ring_size;
> > 
> > -       chan->ring_virt = dma_alloc_coherent(&dma_pdev->dev,
> > +       chan->ring_virt = dma_zalloc_coherent(&dma_pdev->dev,
> >                                              ring_size * sizeof(u64),
> >                                              &chan->ring_dma, GFP_KERNEL);
> >  en
> >         if (!chan->ring_virt)
> >                 return -ENOMEM;
> > 
> > -       memset(chan->ring_virt, 0, ring_size * sizeof(u64));
> > -
> >         return 0;
> >  }
> >  EXPORT_SYMBOL(pasemi_dma_alloc_ring);