linux-kernel - Re: [PATCH v4 1/5] cramfs: direct memory access support

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Date:   Tue, 3 Oct 2017 11:06:30 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
cc:     Alexander Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-embedded@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chris Brandt <Chris.Brandt@...esas.com>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 1/5] cramfs: direct memory access support

On Tue, 3 Oct 2017, Christoph Hellwig wrote:

> On Sun, Oct 01, 2017 at 06:27:11PM -0400, Nicolas Pitre wrote:
> > If you prefer, the physical address could be specified with a Kconfig 
> > symbol just like the kernel link address. Personally I think it is best 
> > to keep it along with the other root mount args. But going all the way 
> > with a dynamic driver binding interface and a dummy intermediate name is 
> > like using a sledge hammer to kill an ant: it will work of course, but 
> > given the context it is prone to errors due to the added manipulations 
> > mentioned previously ... and a tad overkill.
> 
> As soon as a kernel enables CRAMFS_PHYSMEM this mount option is
> available, so you don't just need to think of your use case.

What other use cases do you have in mind?

> The normal way for doings this would be to specify it in the device
> tree.

And specify it how? Creating a pseudo device and passing that instead of 
the actual physical address? What is the advantage?

And what about targets that don't use DT? Yes, there are still quite a 
few out there.


Nicolas