linux-kernel - [PATCH 8/8] mm: comment arm64's usage of 'enum zone

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Message-Id: <20190731154752.16557-9-nsaenzjulienne@suse.de>
Date:   Wed, 31 Jul 2019 17:47:51 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     catalin.marinas@....com, hch@....de, wahrenst@....net,
        marc.zyngier@....com, Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     phill@...pberryi.org, f.fainelli@...il.com, will@...nel.org,
        robh+dt@...nel.org, eric@...olt.net, mbrugger@...e.com,
        nsaenzjulienne@...e.de, akpm@...ux-foundation.org,
        frowand.list@...il.com, m.szyprowski@...sung.com,
        linux-rpi-kernel@...ts.infradead.org
Subject: [PATCH 8/8] mm: comment arm64's usage of 'enum zone_type'

arm64 uses both ZONE_DMA and ZONE_DMA32 for the same reasons x86_64
does: peripherals with different DMA addressing limitations. This
updates both ZONE_DMAs comments to inform about the usage.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>

---

 include/linux/mmzone.h | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index d77d717c620c..8fa6bcf72e7c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -365,23 +365,24 @@ enum zone_type {
 	 *
 	 * Some examples
 	 *
-	 * Architecture		Limit
-	 * ---------------------------
-	 * parisc, ia64, sparc	<4G
-	 * s390, powerpc	<2G
-	 * arm			Various
-	 * alpha		Unlimited or 0-16MB.
+	 * Architecture			Limit
+	 * ----------------------------------
+	 * parisc, ia64, sparc, arm64	<4G
+	 * s390, powerpc		<2G
+	 * arm				Various
+	 * alpha			Unlimited or 0-16MB.
 	 *
 	 * i386, x86_64 and multiple other arches
-	 * 			<16M.
+	 *				<16M.
 	 */
 	ZONE_DMA,
 #endif
 #ifdef CONFIG_ZONE_DMA32
 	/*
-	 * x86_64 needs two ZONE_DMAs because it supports devices that are
-	 * only able to do DMA to the lower 16M but also 32 bit devices that
-	 * can only do DMA areas below 4G.
+	 * x86_64 and arm64 need two ZONE_DMAs because they support devices
+	 * that are only able to DMA a fraction of the 32 bit addressable
+	 * memory area, but also devices that are limited to that whole 32 bit
+	 * area.
 	 */
 	ZONE_DMA32,
 #endif
-- 
2.22.0