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

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Message-ID: <51196161.7020901@wwwdotorg.org>
Date:	Mon, 11 Feb 2013 14:23:45 -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 02:21 PM, Tony Lindgren wrote:
> * Stephen Warren <swarren@...dotorg.org> [130211 13:17]:
>> 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.
> 
> I've seen cases where most of the mux register configuration are
> done correctly by HW engineers.. But there's always been some pieces
> of the pin configuration wrong initially and that needs to be fixed by
> the driver people to get things working.
> 
> Being able to set the mux configuration via debugfs is also very
> useful for the case of adding external devices to your proto boards
> like beagle etc.

This patch won't work for that, since it doesn't support adding new
entries to the mux table, just editing existing entries.

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