linux-kernel - Re: [PATCH] dma-mapping: Relax warnings for per-device areas

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Message-ID: <20180717163330.GE2342@localhost.localdomain>
Date:   Tue, 17 Jul 2018 18:33:30 +0200
From:   Fredrik Noring <noring@...rew.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>, m.szyprowski@...sung.com,
        Geoff Levand <geoff@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        JuergenUrban@....de
Subject: Re: [PATCH] dma-mapping: Relax warnings for per-device areas

Hi Christoph, Geoff,

[ CC-ing Geoff to give him an opportunity to chime in about the PS3 part. ]

> > Here are three other regressions related to the coherent mask WARN_ON_ONCE:
> 
> They are a pretty strong indication that yes, you should really set
> the coherent mask if you ever do coherent allocations..

I'm unfortunately unfamiliar with the USB drivers for the PS3. Geoff, what
do you think about setting a coherent mask?

Christoph, what mask value would you suggest for the PS2 driver? Typical
DMA addresses 0-0x200000 are mapped to 0x1c000000-0x1c200000 and is memory
managed exclusively by the IOP. Robin indicated that DMA_BIT_MASK(20) or a
nonzero but useless value such as 1 are possibly candidates. It seems quite
unclear what the coherent mask actually means in this case, doesn't it?

Fredrik