linux-kernel - [PATCH] cma: decrease CMA_ALIGNMENT lower limit to 2

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Message-Id: <20200930102821.26421-1-paul@crapouillou.net>
Date:   Wed, 30 Sep 2020 12:28:21 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     od@...c.me, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH] cma: decrease CMA_ALIGNMENT lower limit to 2

On an embedded system with a tiny (1 MiB) CMA area for video memory, and
a simple enough video pipeline, we can decrease the CMA_ALIGNMENT by a
factor of 2 to avoid wasting memory, as all the allocations for video
buffers will be of the exact same size (dictated by the size of the
screen).

Signed-off-by: Paul Cercueil <paul@...pouillou.net>
---
 kernel/dma/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 847a9d1fa634..f15e782e19ca 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -162,7 +162,7 @@ endchoice
 
 config CMA_ALIGNMENT
 	int "Maximum PAGE_SIZE order of alignment for contiguous buffers"
-	range 4 12
+	range 2 12
 	default 8
 	help
 	  DMA mapping framework by default aligns all buffers to the smallest
-- 
2.28.0