linux-kernel - Re: [PATCH] regmap: Check readable regs in _regmap

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Date:	Mon, 10 Feb 2014 11:49:27 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, monstr@...str.eu,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] regmap: Check readable regs in _regmap_read

On Mon, Feb 10, 2014 at 11:53:38AM +0100, Lars-Peter Clausen wrote:
> On 02/10/2014 11:46 AM, Michal Simek wrote:
> >Check if regs are readable.

> >+	if (!regmap_readable(map, reg))
> >+		return -EIO;

> This will cause issues with devices where registers are writable,
> but not readable, but we keep the register value in the cache.

Yes, exactly - this is deliberately not done so we can fake up
readability using the cache.  All the 7x9 devices are like this for
example, there's just no read support in the hardware (or if there is
it's not related to the register map).  If we were going to check it
should be at the point where we are about to interact with the hardware.

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