Messages in this thread | | | Date | Fri, 16 Aug 2019 18:36:00 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 6/6] arm64: document the choice of page attributes for pgprot_dmacoherent |
| |
On Fri, Aug 16, 2019 at 06:31:18PM +0100, Will Deacon wrote: > Hi Christoph, > > Thanks for spinning this into a patch. > > On Fri, Aug 16, 2019 at 09:07:54AM +0200, Christoph Hellwig wrote: > > Based on an email from Will Deacon. > > > > Signed-off-by: Christoph Hellwig <hch@lst.de> > > --- > > arch/arm64/include/asm/pgtable.h | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index 6700371227d1..6ff221d9a631 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -435,6 +435,14 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd) > > __pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC) | PTE_PXN | PTE_UXN) > > #define pgprot_device(prot) \ > > __pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_nGnRE) | PTE_PXN | PTE_UXN) > > +/* > > + * DMA allocations for non-coherent devices use what the Arm architecture calls > > + * "Normal non-cacheable" memory, which permits speculation, unaligned accesses > > + * and merging of writes. This is different from "Strongly Ordered" memory > > + * which is intended for MMIO and thus forbids speculation, preserves access > > + * size, requires strict alignment and also forces write responses to come from > > + * the endpoint. > > + */ > > Mind if I tweak the second sentence to be: > > This is different from "Device-nGnR[nE]" memory which is intended for MMIO > and thus forbids speculation, preserves access size, requires strict > alignment and can also force write responses to come from the endpoint. > > ? It's a small change, but it better fits with the arm64 terminology > ("strongly ordered" is no longer used in the architecture). > > If you're happy with that, I can make the change and queue this patch > for 5.4.
FWIW, with that wording:
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
| |