linux-kernel - Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU

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Message-ID: <e908f620-62b8-f106-a1a8-9887f50216fd@landley.net>
Date:   Sat, 27 Jun 2020 20:01:17 -0500
From:   Rob Landley <rob@...dley.net>
To:     Christoph Hellwig <hch@....de>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>
Cc:     linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU

On 6/26/20 3:07 AM, Christoph Hellwig wrote:
> The code handling non-coherent DMA depends on being able to remap code
> as non-cached.  But that can't be done without an MMU, so using this
> option on NOMMU builds is broken.

I'm working on a nommu j-core board that's doing DMA behind the OS's back at the
moment, which I have a todo item to teach the kernel about. The DMA does not go
through the cache, there's currently a cache flush before looking at the result
instead.

How should this be wired up after your patch?

Rob