linux-kernel - [PATCH 1/2] arm64: mm: update the comments about ZONE

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Date:   Sat, 26 Dec 2020 11:35:56 +0800
From:   Chen Zhou <chenzhou10@...wei.com>
To:     <catalin.marinas@....com>, <will@...nel.org>
CC:     <ardb@...nel.org>, <akpm@...ux-foundation.org>, <rppt@...nel.org>,
        <nsaenzjulienne@...e.de>, <song.bao.hua@...ilicon.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <chenzhou10@...wei.com>,
        <huawei.libin@...wei.com>, <xiexiuqi@...wei.com>
Subject: [PATCH 1/2] arm64: mm: update the comments about ZONE_DMA

Since patchset "arm64: Default to 32-bit wide ZONE_DMA", ZONE_DMA's
size is fine-tuned. In the absence of addressing limited masters,
ZONE_DMA will span the whole 32-bit address space, otherwise, in
the case of the Raspberry Pi 4, it'll only span the 30-bit address
space. Update the comments.

Signed-off-by: Chen Zhou <chenzhou10@...wei.com>
---
 arch/arm64/mm/init.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 75addb36354a..7b9809e39927 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -53,10 +53,11 @@ s64 memstart_addr __ro_after_init = -1;
 EXPORT_SYMBOL(memstart_addr);
 
 /*
- * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA covers the first 1G of
- * memory as some devices, namely the Raspberry Pi 4, have peripherals with
- * this limited view of the memory. ZONE_DMA32 will cover the rest of the 32
- * bit addressable memory area.
+ * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA's size is fine-tuned.
+ * In the absence of addressing limited masters, ZONE_DMA will span the
+ * whole 32-bit address space, otherwise, in the case of the Raspberry Pi 4,
+ * it'll only span the 30-bit address space. ZONE_DMA32 will cover the rest
+ * of the 32 bit addressable memory area.
  */
 phys_addr_t arm64_dma_phys_limit __ro_after_init;
 static phys_addr_t arm64_dma32_phys_limit __ro_after_init;
-- 
2.20.1