linux-kernel - Re: [PATCH 1/2] pinctrl: palmas: do not abort pin configuration for BIAS

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Date:	Fri, 27 Sep 2013 10:06:36 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Laxman Dewangan <ldewangan@...dia.com>
CC:	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] pinctrl: palmas: do not abort pin configuration for
 BIAS_DEFAULT

On 09/27/2013 07:30 AM, Laxman Dewangan wrote:
> On Thursday 26 September 2013 09:08 PM, Stephen Warren wrote:
>> On 09/26/2013 06:48 AM, Laxman Dewangan wrote:
>>> Recent movement of all configurations of pin in the single call of
>>> pin_config_set(), it is aborting configuration if BIAS_PULL_PIN_DEFAULT
>>> is selected as return of configuration.
>>>
>>> The original idea was to just avoid any update on register for pull
>>> up/down
>>> configuration if this option is selected.
>> That doesn't sound correct. If a config option is specified in DT or the
>> mapping table, it should be applied to HW. If someone doesn't want a
>> particular config option applied, then it simply shouldn't be mentioned
>> in DT or the mapping table.
>>
>> IIUC, BIAS_DEFAULT should be used only on HW where there is a concept of
>> a true default bias, and in that case, that is what should be applied.
>>
> 
> Hmm.. When I added the PIN_DEFAULT, I just though that do not update
> anything in the register and implemented like that.
> There is nothing "default" option in HW.

The description of that pinconfig option is:

> 7970cb77 (Heiko Stübner    2013-06-06 16:44:25 +0200  43)  * @PIN_CONFIG_BIAS_PULL_PIN_DEFAULT: the pin will be pulled up or down based
> 70637a6d (Heiko Stübner    2013-06-25 14:55:42 +0200  44)  *    on embedded knowledge of the controller hardware, like current mux
> 70637a6d (Heiko Stübner    2013-06-25 14:55:42 +0200  45)  *    function. The pull direction and possibly strength too will normally
> 70637a6d (Heiko Stübner    2013-06-25 14:55:42 +0200  46)  *    be decided completely inside the hardware block and not be readable
> 70637a6d (Heiko Stübner    2013-06-25 14:55:42 +0200  47)  *    from the kernel side.
> 5ca3353b (Linus Walleij    2013-06-16 12:43:06 +0200  48)  *    If the argument is != 0 pull up/down is enabled, if it is 0, the
> 5ca3353b (Linus Walleij    2013-06-16 12:43:06 +0200  49)  *    configuration is ignored. The proper way to disable it is to use
> 5ca3353b (Linus Walleij    2013-06-16 12:43:06 +0200  50)  *    @PIN_CONFIG_BIAS_DISABLE.

If the HW doesn't support any concept of a default pull, I think the
driver shouldn't support that option; it should return an error if asked
to program it.

> In this patch, I just fixed the broken stuff due to recent change.

> However, it the PIN_DEFAULT is not valid option then I need to remove it
> from driver as well as from dt document of Palmas.

Yes.

But what made you come across this issue? Is some pin mapping table or
DT pinctrl node actually using that value? If so, then presumably that
needs to be fixed, as well as removing driver support for that option.

Presumably given this, LinusW shouldn't have actually applied this
patch, since presumably it prevents any other driver from accepting
PIN_CONFIG_BIAS_DISABLE even in cases where it is appropriate?
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