linux-kernel - [RFC 1/3] HACK: ARM: dma-mapping: Get writeback memory for non-consistent mappings

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Date:   Thu, 30 Aug 2018 14:20:28 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     linux-media@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tomasz Figa <tfiga@...omium.org>,
        "Matwey V . Kornilov" <matwey@....msu.ru>,
        Alan Stern <stern@...land.harvard.edu>, kernel@...labora.com,
        Keiichi Watanabe <keiichiw@...omium.org>,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: [RFC 1/3] HACK: ARM: dma-mapping: Get writeback memory for non-consistent mappings

This is obviously a hack.

Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
---
 arch/arm/include/asm/pgtable.h | 3 +++
 arch/arm/mm/dma-mapping.c      | 9 ++++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index a757401129f9..37ddd0d73434 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -122,6 +122,9 @@ extern pgprot_t		pgprot_s2_device;
 #define pgprot_writecombine(prot) \
 	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_BUFFERABLE)
 
+#define pgprot_writeback(prot) \
+	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_WRITEBACK)
+
 #define pgprot_stronglyordered(prot) \
 	__pgprot_modify(prot, L_PTE_MT_MASK, L_PTE_MT_UNCACHED)
 
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 66566472c153..11cca7bbb0a8 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -633,9 +633,12 @@ static void __free_from_contiguous(struct device *dev, struct page *page,
 
 static inline pgprot_t __get_dma_pgprot(unsigned long attrs, pgprot_t prot)
 {
-	prot = (attrs & DMA_ATTR_WRITE_COMBINE) ?
-			pgprot_writecombine(prot) :
-			pgprot_dmacoherent(prot);
+	if (attrs & DMA_ATTR_WRITE_COMBINE)
+		prot = pgprot_writecombine(prot);
+	else if (attrs & DMA_ATTR_NON_CONSISTENT)
+		prot = pgprot_writeback(prot);
+	else
+		prot = pgprot_dmacoherent(prot);
 	return prot;
 }
 
-- 
2.18.0