linux-kernel - Re: [PATCH 1/2] net: can: c_can: Fix default pinmux glitch at init

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Message-ID: <559CFBFB.8010400@ti.com>
Date:	Wed, 8 Jul 2015 13:31:23 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Roger Quadros <rogerq@...com>,
	Marc Kleine-Budde <mkl@...gutronix.de>, <wg@...ndegger.com>,
	<tony@...mide.com>, Tony Lindgren <tony@...mide.com>,
	Linus Walleij <linus.walleij@...aro.org>
CC:	<jay.schroeder@...min.com>, <linux-can@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] net: can: c_can: Fix default pinmux glitch at init

On 07/08/2015 11:13 AM, Roger Quadros wrote:
> 
> On 07/07/15 18:49, Grygorii Strashko wrote:
>> On 07/07/2015 05:37 PM, Roger Quadros wrote:
>>> On 07/07/15 17:35, Roger Quadros wrote:
>>>> On 07/07/15 17:33, Marc Kleine-Budde wrote:
>>>>> On 07/07/2015 04:27 PM, Roger Quadros wrote:
>>>>>> From: "J.D. Schroeder" <jay.schroeder@...min.com>
>>>>>>
>>>>>> The previous change 3973c526ae9c (net: can: c_can: Disable pins when
>>>>>> CAN interface
>>>>>> is down) causes a slight glitch on the pinctrl settings when used.
>>>>>> Since
>>>>>> commit ab78029 (drivers/pinctrl: grab default handles from device
>>>>>> core),
>>>>>> the device core will automatically set the default pins. This causes
>>>>>> the pins to be momentarily set to the default and then to the sleep
>>>>>> state in register_c_can_dev(). By adding an optional "enable" state,
>>>>>> boards can set the default pin state to be disabled and avoid the
>>>>>> glitch when the switch from default to sleep first occurs. If the
>>>>>> "enable" state is not available c_can_pinctrl_select_state() falls
>>>>>> back to using the "default" pinctrl state.
>>>>>>
>>>>>> [Roger Q] - Forward port to v4.2
>>>>>>
>>>>>> Signed-off-by: J.D. Schroeder <jay.schroeder@...min.com>
>>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>>> ---
>>>>>>   drivers/net/can/c_can/c_can.c | 13 ++++++++++++-
>>>>>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/net/can/c_can/c_can.c
>>>>>> b/drivers/net/can/c_can/c_can.c
>>>>>> index 041525d..66e98e7 100644
>>>>>> --- a/drivers/net/can/c_can/c_can.c
>>>>>> +++ b/drivers/net/can/c_can/c_can.c
>>>>>> @@ -605,7 +605,18 @@ static int c_can_start(struct net_device *dev)
>>>>>>       priv->can.state = CAN_STATE_ERROR_ACTIVE;
>>>>>>
>>>>>>       /* activate pins */
>>>>>> -    pinctrl_pm_select_default_state(dev->dev.parent);
>>>>>> +#ifdef CONFIG_PINCTRL
>>>>>
>>>>> Please remove the ifdef, AFAICS there are static inline noop functions
>>>>> if CONFIG_PINCTRL switched off.
>>>>
>>>> yes, you are right.
>>>
>>> On second thoughts
>>>
>>> device->pins are not defined if CONFIG_PINCTRL is not set.
>>> so we can't remove the #ifdef.
>>
>> May be you can use [devm_]pinctrl_get?
> 
> Why should we do that? The device core has already done the 
> pinctrl_get() and it is available in device->pins->p.

True. But It seems, you are going to be only one direct user of pin->p in whole
kernel (outside of pictrl core) !? ;)

pinctrl_get() will just return a pointer on pinctrl associated with dev
if called not the first time and increment kbobj use-counter.

Also, there is nice API pinctrl_get_select() and example in kernel 2c7c2c1d.

So, according to the documentation and pinctrl code, below sequence should work:

struct pinctrl *p;
p = pinctrl_get_select(priv->device, "active");

if (!IS_ERR(p))
   pinctrl_put(p);
else
   pinctrl_pm_select_default_state(priv->device);




>>>>>
>>>>>> +    if (priv->device->pins) {
>>>>>> +        struct pinctrl_state *s;
>>>>>> +
>>>>>> +        /* Attempt to use "active" if available else use 
>>>>>> "default" */
>>>>>> +        s = pinctrl_lookup_state(priv->device->pins->p, "active");
>>>>>> +        if (!IS_ERR(s))
>>>>>> +            pinctrl_select_state(priv->device->pins->p, s);

 ^^ different devices passed here

>>>>>> +        else
>>>>>> +            pinctrl_pm_select_default_state(dev->dev.parent);

^^ and here ? Is it ok?

>>>>>> +    }
>>>>>> +#endif
>>>>>>       return 0;
>>>>>>   }
>>>>>>
>>


-- 
regards,
-grygorii
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