linux-kernel - Re: [PATCH v2 2/2] pinctrl: Allow indicating loss of pin states during low-power

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Date:   Wed, 29 Nov 2017 09:37:26 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Tony Lindgren <tony@...mide.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        linux-gpio@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        Stephen Warren <swarren@...dia.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH v2 2/2] pinctrl: Allow indicating loss of pin states
 during low-power

On 11/29/2017 09:02 AM, Tony Lindgren wrote:
> * Linus Walleij <linus.walleij@...aro.org> [171129 13:03]:
>> On Fri, Nov 3, 2017 at 12:15 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>>> Some platforms (e.g: Broadcom STB: BMIPS_GENERIC/ARCH_BRCMSTB) will lose
>>> their register contents when entering their lower power state. In such a
>>> case, the pinctrl-single driver that is used will not be able to restore
>>> the power states without telling the core about it and having
>>> pinctrl_select_state() check for that.
>>>
>>> This patch adds a new optional boolean property that Device Tree can
>>> define in order to obtain exactly that and having the core pinctrl code
>>> take that into account.
>>>
>>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>>
>> Florian, I'm really sorry for losing track of this patch set, it's
>> important stuff and I see why systems are dependent on something
>> like this.
>>
>> Tony: can you look at this from a pinctrl-single point of view?
>> This is the intended consumer: pinctrl-single users that lose the
>> hardware state over suspend/resume.
>>
>> How do you see this working with other pinctrl-single users?
> 
> Hmm well typically a device driver that loses it's context just does
> save and restore of the registers in runtime PM suspend/resume
> as needed. In this case it would mean duplicating the state for
> potentially for hundreds of registers.. So using the existing
> state in the pinctrl subsystem totally makes sense for the pins.
> 
> Florian do you have other reasons why this should be done in the
> pinctrl framework instead of the driver? Might be worth describing
> the reasoning in the patch descriptions :)

The pinctrl provider driver that I am using is pinctrl-single, which has
proper suspend/resume callbacks but those are not causing any HW
programming to happen because of the (p->state == state) check, hence
this patch series.

> 
> So as long as the pinctrl framework state is used to restore the
> state by the pinctrl driver instead of the pinctrl consumer drivers,
> I don't have issues with this patchset. So probably just improving
> the patch messages a bit should do it.
> 
> FYI, on omaps, the PRCM hardware saves and restores the pinctrl
> state so this has not been so far an issue.
> 
> Regards,
> 
> Tony
> 
> 


-- 
Florian