[PATCH] ARM: Implement pgprot_device()

From: Vincent Whitchurch <vincent.whitchurch@axis.com>
To: linux@armlinux.org.uk
Cc: Vincent Whitchurch <rabinv@axis.com>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: Implement pgprot_device()
Date: Mon, 14 Jan 2019 14:56:38 +0100	[thread overview]
Message-ID: <20190114135638.13520-1-vincent.whitchurch@axis.com> (raw)

This is used when mmapping the PCI resource* files in sys.  Because ARM
currently lacks an implementation of pgprot_device(), it falls back to
pgprot_uncached() (Strongly Ordered), but we should be able to use
Device memory instead.

Doing this speeds up large writes to the resource files by about 40% on
one of my systems.  It also ensures that mmaps on these resources use
the same memory type as ioremap().

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
---
 arch/arm/include/asm/pgtable.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index a757401129f9..48ce1b19069b 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -125,6 +125,9 @@ extern pgprot_t		pgprot_s2_device;
 #define pgprot_stronglyordered(prot) \
 	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_UNCACHED)
 
+#define pgprot_device(prot) \
+	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_DEV_SHARED | L_PTE_SHARED | L_PTE_DIRTY | L_PTE_XN)
+
 #ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
 #define pgprot_dmacoherent(prot) \
 	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_BUFFERABLE | L_PTE_XN)
-- 
2.20.0


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