linux-kernel - Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs

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Date:   Thu, 25 Aug 2022 14:00:32 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
CC:     Alexandre Courbot <gnurou@...il.com>,
        Alexandre Courbot <acourbot@...dia.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Jonathan Corbet <corbet@....net>,
        Russell King <linux@...linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs



Le 25/08/2022 à 15:36, Linus Walleij a écrit :
> On Thu, Aug 18, 2022 at 2:46 PM Arnd Bergmann <arnd@...db.de> wrote:
>> On Thu, Aug 18, 2022 at 2:25 PM Linus Walleij <linus.walleij@...aro.org> wrote:
> 
>>> git grep 'base = -1' yields these suspects:
>>>
>>> arch/arm/common/sa1111.c:       sachip->gc.base = -1;
>>> arch/arm/common/scoop.c:        devptr->gpio.base = -1;
>>> arch/powerpc/platforms/52xx/mpc52xx_gpt.c:      gpt->gc.base = -1;
>>> arch/powerpc/platforms/83xx/mcu_mpc8349emitx.c: gc->base = -1;
>>>
>>> That's all! We could just calculate these to 512-ngpios and
>>> hardcode that instead.
>>
>> How do the consumers find the numbers for these four?
> 
> For SA1111 the chip gets named "sa1111" and some consumers actually
> use proper machine descriptions, maybe all?
> 
> arch/arm/mach-sa1100/jornada720.c:              GPIO_LOOKUP("sa1111",
> 0, "s0-power", GPIO_ACTIVE_HIGH),
> arch/arm/mach-sa1100/jornada720.c:              GPIO_LOOKUP("sa1111",
> 1, "s1-power", GPIO_ACTIVE_HIGH),
> (...)
> 
> For Scoop it is conditionally overridden in the code. I guess always
> overridden.
> 
> For powerpc these seem to be using (old but working) device tree
> lookups, so should not be an issue.
> 
> Sadly I'm not 100% sure that there are no random hard-coded
> GPIO numbers referring to whatever the framework gave them
> at the time the code was written :(

On my PPC board, the one before the last looks suspicious ....

[    0.573261] gpio gpiochip0: registered GPIOs 496 to 511 on 
/soc@...00000/cpm@.../gpio-controller@950
[    0.577460] gpio gpiochip1: registered GPIOs 464 to 495 on 
/soc@...00000/cpm@.../gpio-controller@ab8
[    0.586011] gpio gpiochip2: registered GPIOs 448 to 463 on 
/soc@...00000/cpm@.../gpio-controller@960
[    0.591057] gpio gpiochip3: registered GPIOs 432 to 447 on 
/soc@...00000/cpm@.../gpio-controller@970
[    0.595979] gpio gpiochip4: registered GPIOs 400 to 431 on 
/soc@...00000/cpm@.../gpio-controller@ac8
[    0.629292] gpio_stub_drv gpiochip5: registered GPIOs 384 to 399 on 
/localbus@...00100/cpld-cmpc@5,0000000/gpio-controller@2
[    0.636556] gpio_stub_drv gpiochip6: registered GPIOs 368 to 383 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@00
[    0.639503] gpio_stub_drv gpiochip7: registered GPIOs 352 to 367 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@02
[    0.642434] gpio_stub_drv gpiochip8: registered GPIOs 336 to 351 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@04
[    0.645257] gpio_stub_drv gpiochip9: registered GPIOs 320 to 335 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@10
[    0.648230] gpio_stub_drv gpiochip10: registered GPIOs 304 to 319 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@20
[    0.651070] gpio_stub_drv gpiochip11: registered GPIOs 288 to 303 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@22
[    0.653986] gpio_stub_drv gpiochip12: registered GPIOs 272 to 287 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@24
[    0.656807] gpio_stub_drv gpiochip13: registered GPIOs 256 to 271 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@26
[    0.659761] gpio_stub_drv gpiochip14: registered GPIOs 240 to 255 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@28
[    0.662622] gpio_stub_drv gpiochip15: registered GPIOs 224 to 239 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@2A
[    0.665454] gpio_stub_drv gpiochip16: registered GPIOs 208 to 223 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@2C
[    0.673552] gpio_stub_drv gpiochip17: registered GPIOs 192 to 207 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@30
[    0.677281] gpio_stub_drv gpiochip18: registered GPIOs 176 to 191 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@32
[    0.680235] gpio_stub_drv gpiochip19: registered GPIOs 160 to 175 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@40
[    0.685876] gpio_stub_drv gpiochip20: registered GPIOs 144 to 159 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@42
[    0.694431] gpio_stub_drv gpiochip21: registered GPIOs 128 to 143 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@44
[    0.697257] gpio_stub_drv gpiochip22: registered GPIOs 112 to 127 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@50
[    0.700220] gpio_stub_drv gpiochip23: registered GPIOs 96 to 111 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@52
[    0.703183] gpio_stub_drv gpiochip24: registered GPIOs 80 to 95 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@54
[    0.708226] gpio_stub_drv gpiochip25: registered GPIOs 64 to 79 on 
/localbus@...00100/fpga-m@4,0000000/gpio-controller@34
[    0.756817] gpio gpiochip26: registered GPIOs 0 to 2 on generic
[    4.530397] gpio gpiochip27: registered GPIOs 36 to 63 on max7301


> 
> Another reason the base is assigned from above (usually
> from 512 and downward) is that the primary SoC GPIO usually
> want to be at base 0 and there is no guarantee that it will
> get probed first. So hard-coded GPIO bases go from 0 -> n
> and dynamically allocateed GPIO bases from n <- 512.
> 
> Then we hope they don't meet and overlap in the middle...
> 
>>> and in that case it is better to delete the use of this function
>>> altogether since it can not fail.
>>
>> S32_MAX might be a better upper bound. That allows to
>> just have no number assigned to a gpio chip. Any driver
>> code calling desc_to_gpio() could then get back -1
>> or a negative error code.
>>
>> Making the ones that are invalid today valid sounds like
>> a step backwards to me if the goal is to stop using
>> gpio numbers and most consumers no longer need them.
> 
> OK I get it...
> 
> Now: who wants to write this patch? :)
> 
> Christophe? Will you take a stab at it?
> 


Which patch should I write ?

Christophe