linux-kernel - Re: [PATCH] sparc32: Page align size in arch_dma

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Date:   Tue, 14 Sep 2021 10:51:51 +0200
From:   Andreas Larsson <andreas@...sler.com>
To:     Christoph Hellwig <hch@....de>
Cc:     David Miller <davem@...emloft.net>, sparclinux@...r.kernel.org,
        Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org,
        software@...sler.com
Subject: Re: [PATCH] sparc32: Page align size in arch_dma_alloc

On 2021-09-14 08:17, Christoph Hellwig wrote:
> Thanks.  Can you take a look and test the two patches below on top of
> your fix?  A git tree is also available here:
> 
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/sparc32-generic-dma
> 

In a quick test, this seems to work on LEON for code paths previously 
going to arch_dma_alloc and arch_dma_free. However, this makes setting 
up these DMA mappings to not go through sparc_dma_alloc_resource, and it 
seems important that they do that on Sun systems. Hopefully, someone 
with more knowledge about that could chime in here.

The added pgprot_dmacoherent is problematic as it sets SRMMU_PRIV, which 
sets up kernel access only. This was fine for arch_dma_alloc that sets 
up kernel accesses only, but for user space DMA mmap this would make 
them kernel accessable only. Having no sparc-specific 
pgprot_dmacoherent, keeping it to default to pgprot_noncached, is 
probably better.

-- 
Andreas Larsson