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From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: linux-arm-kernel@lists.infradead.org
Cc: Stefan Wahren <stefan.wahren@i2se.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	will@kernel.org
Subject: Limiting the DMA zone in arm64
Date: Thu, 11 Jul 2019 11:51:57 +0200	[thread overview]
Message-ID: <0439cc08532849b1d0adb44a7b2cbc9ce5dceaf7.camel@suse.de> (raw)

Hi,
I'm trying to bring up the new RPi4 on arm64, and running into issues with DMA
allocations. The device has up to 4GB of ram, but AFAIK only the first GB of
ram can be used for DMA: the DMA address range is 0xc0000000-0xffffffff which
is aliased to the first GB of memory 0x00000000-0x40000000.

This is solved in arm32 using a board file with '.dma_zone_size = SZ_1G'. But I
haven't found any similar mechanism for arm64. Any suggestions?

Just it case it helps understand the issue, I managed to get things going by
doing the following:

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index f3c795278def..ec3cb7b76a76 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -407,7 +407,8 @@ void __init arm64_memblock_init(void)
 
        /* 4GB maximum for 32-bit only capable devices */
        if (IS_ENABLED(CONFIG_ZONE_DMA32))
-               arm64_dma_phys_limit = max_zone_dma_phys();
+               arm64_dma_phys_limit = 0x40000000;
        else
                arm64_dma_phys_limit = PHYS_MASK + 1;

Regards,
Nicolas



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             reply	other threads:[~2019-07-11  9:52 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-11  9:51 Nicolas Saenz Julienne [this message]
2019-07-11 10:15 ` Limiting the DMA zone in arm64 Jisheng Zhang
2019-07-11 10:17   ` Nicolas Saenz Julienne
2019-07-11 10:17 ` Will Deacon
2019-07-11 11:10   ` Nicolas Saenz Julienne
2019-07-11 13:32     ` Phil Elwell

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