linux-kernel - Re: [PATCH] gpiolib: fix allocation of mixed dynamic/static GPIOs

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Date:   Thu, 27 Apr 2023 10:55:57 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Andreas Kemnade <andreas@...nade.info>
CC:     "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        ": Tony Lindgren" <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: fix allocation of mixed dynamic/static GPIOs



Le 27/04/2023 à 12:46, Andy Shevchenko a écrit :
> On Thu, Apr 27, 2023 at 1:37 PM Andreas Kemnade <andreas@...nade.info> wrote:
>>
>> On Thu, 27 Apr 2023 06:20:34 +0000
>> Christophe Leroy <christophe.leroy@...roup.eu> wrote:
>>
>>> Le 27/04/2023 à 08:00, Andy Shevchenko a écrit :
>>>> On Thu, Apr 27, 2023 at 8:40 AM Christophe Leroy
>>>> <christophe.leroy@...roup.eu> wrote:
>>>>>
>>>>>
>>>>>
>>>>> Le 27/04/2023 à 00:03, Andreas Kemnade a écrit :
>>>>>> [Vous ne recevez pas souvent de courriers de andreas@...nade.info. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>>>>>
>>>>>> If static allocation and dynamic allocation GPIOs are present,
>>>>>> dynamic allocation pollutes the numberspace for static allocation,
>>>>>> causing static allocation to fail.
>>>>>> Enfore dynamic allocation above GPIO_DYNAMIC_BASE.
>>>>>
>>>>> Hum ....
>>>>>
>>>>> Commit 7b61212f2a07 ("gpiolib: Get rid of ARCH_NR_GPIOS") was supposed
>>>>> to enforce dynamic allocation above GPIO_DYNAMIC_BASE already.
>>>>>
>>>>> Can you describe what is going wrong exactly with the above commit ?
>>>>
>>>> Above commit only works to the first dynamic allocation, if you need
>>>> more than one with static ones present it mistakenly will give you a
>>>> base _below_ DYNAMIC_BASE.
>>>
>>> Ah right, that needs to be fixed.
>>>
>>>>
>>>> However, this change is just PoC I proposed, the conditional and
>>>> action should be slightly different to cover a corner case, when
>>>> statically allocated chip overlaps the DYNAMIC_BASE, i.e. gdev->base <
>>>> DYNAMIC_BASE, while gdev->base + gdev->ngpio >= DYNAMIC_BASE.
>>>>
>>>
>>> Yes you are right, that's gdev->base + gdev->ngpio that should be checked.
>>>
>> and that not with simple continue or base might simply stay at DYNAMIC_BASE.
>>
>> I will send a v2 of this patch with refined logic.
> 
> Actually it would be nice to integrate a warning (if we don't have it
> yet) when adding a GPIO chip with a static allocation and which will
> overlap the dynamic base. Can you add that into your v2?
> 

At the time being we have a warning for all static allocations, 
allthough their has been some discussion about reverting it, see commit 
502df79b8605 ("gpiolib: Warn on drivers still using static gpiobase 
allocation")

Christophe