linux-kernel - Re: Re: [PATCH] [PATCH] ARM64: Setup DMA32 zone size by bootargs

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Message-ID: <20200924141514.23930-1-phil.chang@mediatek.com>
Date:   Thu, 24 Sep 2020 22:15:14 +0800
From:   Phil Chang <phil.chang@...iatek.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        Phil Chang <phil.chang@...iatek.com>,
        YJ Chiang <yj.chiang@...iatek.com>,
        Alix Wu <alix.wu@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: Re: [PATCH] [PATCH] ARM64: Setup DMA32 zone size by bootargs

Actually, In a embedded system with 3GB memory, the memory bus width is not the same among the 3GB.
(The first 2GB is 48-bit wide, and the latter 1GB is 16-bit wide.)
For memory throughput reason of hardware IPs, we need allocate memory from the first 2GB for
the hardware IPs. And that is why we setup the first 2GB as DMA_ZONE, and use GFP_DMA to allocate
memory from the range.