From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] pinctrl: document the pinctrl PM states
Date: Mon, 24 Jun 2013 12:09:24 -0600 [thread overview]
Message-ID: <51C88B54.9000902@wwwdotorg.org> (raw)
In-Reply-To: <20130624101055.GT5523@atomide.com>
On 06/24/2013 04:10 AM, Tony Lindgren wrote:
> * Stephen Warren <swarren@wwwdotorg•org> [130621 12:18]:
>> On 06/21/2013 12:25 AM, Tony Lindgren wrote:
>>> * Stephen Warren <swarren@wwwdotorg•org> [130620 12:32]:
>>>>
>>>> I assume you mean there shouldn't be any issue *modifying* the pinctrl
>>>> API to allow multiple states to be active at once? And where you're
>>>> talking about having multiple sets active at once already, you're
>>>> talking about some other API?
>>>
>>> Nope, the standard pinctrl API. At least I have not seen issues with
>>> having multiple states active the same time in a single driver.
>>
>> Please take a look at the implementation of pinctrl_select_state(). It
>> very explicitly performs the following steps:
>>
>> 1) Find all pins(groups) that are used in the current state but not the
>> new state, and execute pinctrl_disable_setting() on them. (For mux
>> settings only, not pin config, since the core doesn't have any idea how
>> to reverse config settings).
>>
>> 2) For all settings in the new state, apply those settings.
>>
>> So, it very explicitly only allows a single state to be set at a time.
>> Equally, p->state (the field which stores the currently selected state)
>> is a single item, not a set/list/array.
>
> OK thanks I get now what you're saying. I did not see the p->state
> issue as the disable function won't do anything for the SoCs that I
> mostly deal with.
>
>> So, this code needs rework if you want the core to support the concept
>> of having multiple states active at once, since it needs separate
>> pinctrl_activate_state() and pinctrl_deactivate_state() APIs, in order
>> to avoid step (1) above. And of course, p->state would need to be a
>> set/list/array.
>
> I'll think about it a bit and do a patch to fix this. It seems that
> that we need just two entries in the p->state array: static (default),
> and dynamic. Then the dynamic would be typically one of: active, idle,
> rx, tx.
I'm not entirely convinced that "2" is the right number. If we start
allowing drivers to "piece together" multiple different state names, why
wouldn't you allow 3 (or n) different state names to be active at once?
Off-hand, I don't have specific use-cases in mind for more than 2 state
(or even 1 in my case I suspect) - it just seems like expecting to
arbitrarily restrict the number of co-active states is unlikely to last
for long, and it'll end up being a slippery slope.
next prev parent reply other threads:[~2013-06-24 18:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-11 19:59 [PATCH] pinctrl: document the pinctrl PM states Linus Walleij
2013-06-12 18:37 ` Tony Lindgren
2013-06-13 19:39 ` Stephen Warren
2013-06-13 20:34 ` Linus Walleij
2013-06-14 15:43 ` Stephen Warren
2013-06-16 10:17 ` Linus Walleij
2013-06-17 7:20 ` Tony Lindgren
2013-06-17 15:56 ` Linus Walleij
2013-06-17 18:06 ` Tony Lindgren
2013-06-17 18:15 ` Rohit Vaswani
2013-06-17 16:05 ` Linus Walleij
2013-06-17 18:02 ` Tony Lindgren
2013-06-19 20:06 ` Stephen Warren
2013-06-24 12:37 ` Linus Walleij
2013-06-25 7:31 ` Tony Lindgren
2013-06-19 20:02 ` Stephen Warren
2013-06-20 6:38 ` Tony Lindgren
2013-06-20 19:26 ` Stephen Warren
2013-06-21 6:25 ` Tony Lindgren
2013-06-21 19:12 ` Stephen Warren
2013-06-24 10:10 ` Tony Lindgren
2013-06-24 18:09 ` Stephen Warren [this message]
2013-06-25 7:38 ` Tony Lindgren
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