linux-kernel - Re: [RFC PATCH] RFC: drivers: gpio: helper for generic pin IRQ handling

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Date:   Thu, 10 Dec 2020 17:40:05 +0200
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        <joyce.ooi@...el.com>, Andrew Jeffery <andrew@...id.au>,
        Hoan Tran <hoan@...amperecomputing.com>,
        Serge Semin <fancer.lancer@...il.com>, <orsonzhai@...il.com>,
        <baolin.wang7@...il.com>, <zhang.lyra@...il.com>,
        Andy Shevchenko <andy@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Jun Nie <jun.nie@...aro.org>, Shawn Guo <shawnguo@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>
Subject: Re: [RFC PATCH] RFC: drivers: gpio: helper for generic pin IRQ
 handling



On 09/12/2020 12:23, Enrico Weigelt, metux IT consult wrote:
> On 08.12.20 17:18, Grygorii Strashko wrote:
> 
>>>>> Having all GPIO drivers doing their IRQ management entirely through the
>>>>> GPIO subsystem (eg. never calling generic_handle_irq() and using the
>>>>> builtin
>>>>> IRQ handling) would also allow a more direct (eg. callback-based)
>>>>> pin change
>>>>> notification for GPIO consumers, that doesn't involve registering
>>>>> them as
>>>>> generic IRQ handlers.
>>
>> Above part makes me worry - why?
> 
> Why so ?
> 
> Little clarification, in case i've been a bit confusion - there're two
> separate topics:
> 
> a) consolidating repeated patterns (eg. calling the actual irq handling)
>     into gpiolib, (and later possibly use more fields already existing in
>     struct gpio_chip for irq handling)

Even if there is some pattern It doesn't mean consolidation is always reasonable.
one of the things to think about is compiler optimization and will/will not this change
add additional

> 
> b) a direct consumer callback for change, where the consumer doesn't
>     have to care about IRQs at all (some drivers could even do polling,
>     when hw doesn't have IRQs). This is for consumers that don't use
>     GPIOs as interrupt source, but more more like a very raw serial port,
>     eg. bitbanging of other interfaces (maybe an gpio bus type ? ;-))

in his case they do polling, so what's the issue with this?

or you want gpio-controller to do polling for you?

Actually there are few types of consumers:
- gpio users, no irq
- irq users, no gpio
- gpio users and irq users
- and finally (only few) use the same gpio as gpio and as an irq,
   including dynamic direction change.

> 
> The above paragraph just outlines that b) might be much easier to
> implement, once the suggested refactoring is done and no driver would
> call irq handlers directly anymore. But this hasn't much to do with
> the proposal itself, just an idea for future use.
> 
> --mtx
> 

-- 
Best regards,
grygorii