linux-kernel - Re: [PATCH 4/4] pinctrl: re-enable old state in case of error in pinctrl_select

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Date:	Thu, 28 Mar 2013 11:38:23 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Richard GENOUD <richard.genoud@...il.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Stephen Warren <swarren@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] pinctrl: re-enable old state in case of error in
 pinctrl_select_state

On 03/28/2013 11:34 AM, Richard GENOUD wrote:
> On [mer., 27.03.2013 17:55:45], Stephen Warren wrote:
>> On 03/25/2013 08:47 AM, Richard Genoud wrote:
>>> If a new state is applied, the groups configured in the old state but
>>> not in the new state are disabled.
>>> If something goes wrong and the new state can't be applied, we have to
>>> re-enable those groups.
>>
>> What is the use-case for this? I wonder if it isn't better to simply
>> undo the partial selection of the new state (as patch 3/4 attempts to
>> do) and then leave p->state==NULL, indicating that no state is actively
>> selected. IIRC, this would be the same as right after the initial
>> pinctrl_select().
>>
>> I wonder if it's likely that attempting to re-apply the old state would
>> actually work, given that applying something just failed.
>>
>> Finally, this recovery code doesn't:
>>
>> a) Process anything except MUX_GROUP; any pin config settings in the old
>> state aren't restored.
>>
>> b) (I think) Apply any mux settings that don't involve groups that are
>> referenced by both the old and new states; given that patch 3/4 attempts
>> to undo everything in the failed application of the new state, I think
>> this "re-apply the old state" code should simple run through everything
>> in the old state any apply it unconditionally.
>
> So, if I understand correctly, it could be as simple as that:
>  	}
>  
> -	if (old_state) {
> -		list_for_each_entry(setting, &old_state->settings, node) {
> -			bool found = false;
> -			if (setting->type != PIN_MAP_TYPE_MUX_GROUP)
> -				continue;
> -			list_for_each_entry(setting2, &state->settings, node) {
> -				if (setting2->type != PIN_MAP_TYPE_MUX_GROUP)
> -					continue;
> -				if (setting2->data.mux.group ==
> -						setting->data.mux.group) {
> -					found = true;
> -					break;
> -				}
> -			}
> -			if (!found)
> -				pinmux_enable_setting(setting);
> -		}
> -	}
> -
>  	p->state = old_state;

I think you want to remove that line too, so that p->state == NULL in
the error case, so that if the pinctrl_select_state_locked() call below
also fails to restore the old state, then (!old_state) will be true
inside the recursive call, so it doesn't recurse into itself forever.

> +	if (old_state)
> +		pinctrl_select_state_locked(p, NULL);

You want to pass old_state rather than NULL there, I think.
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