linux-kernel - Re: [PATCH 2/2] regmap: Fix permissions on debugfs cache controls

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Date:	Fri, 5 Jun 2015 16:25:37 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Richard Fitzgerald <rf@...nsource.wolfsonmicro.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	patches@...nsource.wolfsonmicro.com
Subject: Re: [PATCH 2/2] regmap: Fix permissions on debugfs cache controls

On Fri, Jun 05, 2015 at 03:34:46PM +0100, Richard Fitzgerald wrote:
> The cache_only and cache_bypass debugfs entries are expected
> to be writable by user-side but are set to read-only permissions.

Your expectation is not my expectation here :)   The permissions here
are quite deliberate.

> This is only working accidentally because debugfs doesn't currently
> honour the read-only bit.

Honestly it wasn't supposed to be working at all.  We can have a
discussion about if it makes sense for it to work, that's not a totally
unreasonable thing though I'd really want to taint the kernel if anyone
actually does it (particularly for cache only) since it seems even more
likely to interact poorly with drivers than random register writes.

We'll also want to sync the cache when transitioning from cache only to
normal operation I think, or provide a way of doing that.

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