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

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Date:	Wed, 8 Jul 2015 13:44:53 +0300
From:	Roger Quadros <rogerq@...com>
To:	Grygorii Strashko <grygorii.strashko@...com>,
	Marc Kleine-Budde <mkl@...gutronix.de>, <wg@...ndegger.com>,
	<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 08/07/15 13:31, Grygorii Strashko wrote:
> 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) !? ;)

good point :).

> 
> 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);

This is much neater. I will give that a try. Thanks.

cheers,
-roger

> 
> 
> 
> 
>>>>>>
>>>>>>> +    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;
>>>>>>>   }
>>>>>>>
>>>
> 
> 
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