linux-kernel - Re: [PATCH] pinctrl/pinconfig: add debug interface

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Message-ID: <51195F00.4020309@wwwdotorg.org>
Date:	Mon, 11 Feb 2013 14:13:36 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tony Lindgren <tony@...mide.com>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>,
	Laurent Meunier <laurent.meunier@...com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] pinctrl/pinconfig: add debug interface

On 02/11/2013 02:00 PM, Tony Lindgren wrote:
> * Stephen Warren <swarren@...dotorg.org> [130211 12:57]:
>> On 02/10/2013 01:11 PM, Linus Walleij wrote:
>>> From: Laurent Meunier <laurent.meunier@...com>
>>>
>>> This update adds a debugfs interface to modify a pin configuration
>>> for a given state in the pinctrl map. This allows to modify the
>>> configuration for a non-active state, typically sleep state.
>>> This configuration is not applied right away, but only when the state
>>> will be entered.
>>>
>>> This solution is mandated for us by HW validation: in order
>>> to test and verify several pin configurations during sleep without
>>> recompiling the software.
>>
>> I never understood why HW engineers can't just recompile the kernel.
>> Besides, it's just a device tree change these days - no recompile even
>> required, right?
> 
> Typically when bringing up a new board you do not have the driver
> specific mux settings verified. For developers, it's easiest to tweak
> the muxing during runtime do the drivers as a loadable module, then
> export the verified mux configuration into a .dts file.

Well HW engineers typically just write to the HW registers directly
rather than screwing around with the Linux pinctrl tables and
unloading/reloading drivers.
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