linux-kernel - [PATCH 1/8] dma-mapping: add DMA_ATTR_LOW

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Message-Id: <20200925141218.13550-2-m.szyprowski@samsung.com>
Date:   Fri, 25 Sep 2020 16:12:11 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Linux IOMMU <iommu@...ts.linux-foundation.org>,
        linux-media@...r.kernel.org, linux-samsung-soc@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Christoph Hellwig <hch@....de>,
        Sylwester Nawrocki <snawrocki@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/8] dma-mapping: add DMA_ATTR_LOW_ADDRESS attribute

Some devices require to allocate a special buffer (usually for the
firmware) just at the beginning of the address space to ensure that all
further allocations can be expressed as a positive offset from that
special buffer. When IOMMU is used for managing the DMA address space,
such requirement can be easily fulfilled, simply by enforcing the
'first-fit' IOVA allocation algorithm.

This patch adds a DMA attribute for such case.

Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
---
 include/linux/dma-mapping.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index bb138ac6f5e6..c8c568ba375b 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -66,6 +66,12 @@
  * at least read-only at lesser-privileged levels).
  */
 #define DMA_ATTR_PRIVILEGED		(1UL << 9)
+/*
+ * DMA_ATTR_LOW_ADDRESS: used to indicate that the buffer should be allocated
+ * at the lowest possible DMA address, usually just at the beginning of the
+ * DMA/IOVA address space ('first-fit' allocation algorithm).
+ */
+#define DMA_ATTR_LOW_ADDRESS		(1UL << 10)
 
 /*
  * A dma_addr_t can hold any valid DMA or bus address for the platform.
-- 
2.17.1