* document dma-direct zone selection
@ 2018-10-01 20:10 Christoph Hellwig
2018-10-01 20:10 ` [PATCH] dma-direct: document the zone selection logic Christoph Hellwig
0 siblings, 1 reply; 5+ messages in thread
From: Christoph Hellwig @ 2018-10-01 20:10 UTC (permalink / raw)
To: iommu
Cc: Marek Szyprowski, Robin Murphy, Benjamin Herrenschmidt, linux-kernel
Hi all,
this patch documents the dma-direct zone selection, as it doesn't
seem quite obvuious enough.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] dma-direct: document the zone selection logic
2018-10-01 20:10 document dma-direct zone selection Christoph Hellwig
@ 2018-10-01 20:10 ` Christoph Hellwig
2018-10-01 20:22 ` Randy Dunlap
2018-10-08 7:03 ` Christoph Hellwig
0 siblings, 2 replies; 5+ messages in thread
From: Christoph Hellwig @ 2018-10-01 20:10 UTC (permalink / raw)
To: iommu
Cc: Marek Szyprowski, Robin Murphy, Benjamin Herrenschmidt, linux-kernel
What we are doing here isn't quite obvious, so add a comment explaining
it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
kernel/dma/direct.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index ba6f5956a291..14b966e2349a 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
else
*phys_mask = dma_to_phys(dev, dma_mask);
- /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
+ /*
+ * Optimistically try the zone that the physicall address mask falls
+ * into first. If that returns memory that isn't actually addressable
+ * we will fallback to the next lower zone and try again.
+ *
+ * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
+ * zones.
+ */
if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
return GFP_DMA;
if (*phys_mask <= DMA_BIT_MASK(32))
--
2.19.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] dma-direct: document the zone selection logic
2018-10-01 20:10 ` [PATCH] dma-direct: document the zone selection logic Christoph Hellwig
@ 2018-10-01 20:22 ` Randy Dunlap
2018-10-08 7:03 ` Christoph Hellwig
1 sibling, 0 replies; 5+ messages in thread
From: Randy Dunlap @ 2018-10-01 20:22 UTC (permalink / raw)
To: Christoph Hellwig, iommu
Cc: Marek Szyprowski, Robin Murphy, Benjamin Herrenschmidt, linux-kernel
On 10/1/18 1:10 PM, Christoph Hellwig wrote:
> What we are doing here isn't quite obvious, so add a comment explaining
> it.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> kernel/dma/direct.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index ba6f5956a291..14b966e2349a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> else
> *phys_mask = dma_to_phys(dev, dma_mask);
>
> - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> + /*
> + * Optimistically try the zone that the physicall address mask falls
physical
> + * into first. If that returns memory that isn't actually addressable
> + * we will fallback to the next lower zone and try again.
> + *
> + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
> + * zones.
> + */
> if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> return GFP_DMA;
> if (*phys_mask <= DMA_BIT_MASK(32))
>
thanks for the documentation.
--
~Randy
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] dma-direct: document the zone selection logic
2018-10-01 20:10 ` [PATCH] dma-direct: document the zone selection logic Christoph Hellwig
2018-10-01 20:22 ` Randy Dunlap
@ 2018-10-08 7:03 ` Christoph Hellwig
2018-10-08 22:56 ` Benjamin Herrenschmidt
1 sibling, 1 reply; 5+ messages in thread
From: Christoph Hellwig @ 2018-10-08 7:03 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: iommu, Robin Murphy, linux-kernel
Ben, does this resolve your issues with the confusing zone selection?
On Mon, Oct 01, 2018 at 01:10:16PM -0700, Christoph Hellwig wrote:
> What we are doing here isn't quite obvious, so add a comment explaining
> it.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> kernel/dma/direct.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index ba6f5956a291..14b966e2349a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> else
> *phys_mask = dma_to_phys(dev, dma_mask);
>
> - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> + /*
> + * Optimistically try the zone that the physicall address mask falls
> + * into first. If that returns memory that isn't actually addressable
> + * we will fallback to the next lower zone and try again.
> + *
> + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
> + * zones.
> + */
> if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> return GFP_DMA;
> if (*phys_mask <= DMA_BIT_MASK(32))
> --
> 2.19.0
>
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
---end quoted text---
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] dma-direct: document the zone selection logic
2018-10-08 7:03 ` Christoph Hellwig
@ 2018-10-08 22:56 ` Benjamin Herrenschmidt
0 siblings, 0 replies; 5+ messages in thread
From: Benjamin Herrenschmidt @ 2018-10-08 22:56 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: iommu, Robin Murphy, linux-kernel
On Mon, 2018-10-08 at 09:03 +0200, Christoph Hellwig wrote:
> Ben, does this resolve your issues with the confusing zone selection?
The comment does make things a tad clearer yes :)
Thanks !
Cheers,
Ben.
> On Mon, Oct 01, 2018 at 01:10:16PM -0700, Christoph Hellwig wrote:
> > What we are doing here isn't quite obvious, so add a comment explaining
> > it.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > kernel/dma/direct.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index ba6f5956a291..14b966e2349a 100644
> > --- a/kernel/dma/direct.c
> > +++ b/kernel/dma/direct.c
> > @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> > else
> > *phys_mask = dma_to_phys(dev, dma_mask);
> >
> > - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> > + /*
> > + * Optimistically try the zone that the physicall address mask falls
> > + * into first. If that returns memory that isn't actually addressable
> > + * we will fallback to the next lower zone and try again.
> > + *
> > + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding
> > + * zones.
> > + */
> > if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> > return GFP_DMA;
> > if (*phys_mask <= DMA_BIT_MASK(32))
> > --
> > 2.19.0
> >
> > _______________________________________________
> > iommu mailing list
> > iommu@lists.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
> ---end quoted text---
^ permalink raw reply [flat|nested] 5+ messages in thread
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