From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Date: Tue, 30 Apr 2019 20:29:47 +0000
Subject: Re: [PATCH 5/7] MIPS: use the generic uncached segment support in dma-direct
Message-Id: <20190430202947.GA30262@lst.de>
List-Id: <linux-fbdev.vger.kernel.org>
References: <20190430110032.25301-1-hch@lst.de> <20190430110032.25301-6-hch@lst.de> <20190430201041.536amvinrcvd2wua@pburton-laptop>
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To: Paul Burton <paul.burton@mips.com>
Cc: Christoph Hellwig <hch@lst.de>, Ralf Baechle <ralf@linux-mips.org>, James Hogan <jhogan@kernel.org>, Ley Foon Tan <lftan@altera.com>, Michal Simek <monstr@monstr.eu>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>, "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>

On Tue, Apr 30, 2019 at 08:10:43PM +0000, Paul Burton wrote:
> This series looks like a nice cleanup to me - the one thing that puzzles
> me is the !PageHighMem check above.
> 
> As far as I can see arch_dma_prep_coherent() should never be called with
> a highmem page, so would it make more sense to either drop this check or
> perhaps wrap it in a WARN_ON()?

dma_alloc_from_contigous can return highmem pages depending on where
the CMA area is located.  But given that these pages don't have a
direct kernel mapping we also shouldn't have to flush the caches
for them.