linux-kernel - Re: [PATCH v3 2/4] leds: simatic-ipc-leds: add new driver for Siemens Industial PCs

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Date:   Tue, 30 Mar 2021 15:41:53 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Henning Schild <henning.schild@...mens.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-watchdog@...r.kernel.org,
        Srikanth Krishnakar <skrishnakar@...il.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Gerd Haeussler <gerd.haeussler.ext@...mens.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Pavel Machek <pavel@....cz>, Enrico Weigelt <lkml@...ux.net>
Subject: Re: [PATCH v3 2/4] leds: simatic-ipc-leds: add new driver for Siemens
 Industial PCs

On Tue, Mar 30, 2021 at 3:35 PM Henning Schild
<henning.schild@...mens.com> wrote:
> Am Tue, 30 Mar 2021 15:15:16 +0300
> schrieb Andy Shevchenko <andy.shevchenko@...il.com>:
> > On Tue, Mar 30, 2021 at 2:58 PM Henning Schild
> > <henning.schild@...mens.com> wrote:
> > > Am Tue, 30 Mar 2021 14:04:35 +0300
> > > schrieb Andy Shevchenko <andy.shevchenko@...il.com>:
> > > > On Mon, Mar 29, 2021 at 8:59 PM Henning Schild
> > > > <henning.schild@...mens.com> wrote:

> > > > > +static struct simatic_ipc_led simatic_ipc_leds_mem[] = {
> > > > > +       {0x500 + 0x1A0, "red:" LED_FUNCTION_STATUS "-1"},
> > > > > +       {0x500 + 0x1A8, "green:" LED_FUNCTION_STATUS "-1"},
> > > > > +       {0x500 + 0x1C8, "red:" LED_FUNCTION_STATUS "-2"},
> > > > > +       {0x500 + 0x1D0, "green:" LED_FUNCTION_STATUS "-2"},
> > > > > +       {0x500 + 0x1E0, "red:" LED_FUNCTION_STATUS "-3"},
> > > > > +       {0x500 + 0x198, "green:" LED_FUNCTION_STATUS "-3"},
> > > > > +       { }
> > > > > +};
> > > >
> > > > It seems to me like poking GPIO controller registers directly.
> > > > This is not good. The question still remains: Can we simply
> > > > register a GPIO (pin control) driver and use an LED GPIO driver
> > > > with an additional board file that instantiates it?
> > >
> > > I wrote about that in reply to the cover letter. My view is still
> > > that it would be an abstraction with only one user, just causing
> > > work and likely not ending up as generic as it might eventually
> > > have to be.
> > >
> > > The region is reserved, not sure what the problem with the "poking"
> > > is.
> >
> >
> > > Maybe i do not understand all the benefits of such a split at this
> > > point in time. At the moment i only see work with hardly any
> > > benefit, not just work for me but also for maintainers. I sure do
> > > not mean to be ignorant. Maybe you go into details and convince me
> > > or we wait for other peoples opinions on how to proceed, maybe
> > > there is a second user that i am not aware of?
> > > Until i am convinced otherwise i will try to argue that a
> > > single-user-abstraction is needless work/code, and should be done
> > > only when actually needed.
> >
> > I have just read your messages (there is a cover letter and additional
> > email which was sent lately).
> >
> > I would like to know what the CPU model number on that board is. Than
> > we can continue to see what possibilities we have here.
>
> I guess we are talking about the one that uses memory mapped, that is
> called an "IPC127E" and seems to have either Intel Atom E3940 or E3930
> which seems to be Apollo Lake.

Yep. And now the question, in my patch series you should have got the
apollolake-pinctrl driver loaded (if not, we have to investigate why
it's not being instantiated). This will give you a read GPIO driver.
So, you may use regular LED GPIO on top of it
(https://elixir.bootlin.com/linux/latest/source/drivers/leds/leds-gpio.c).
I would like to understand why it can't be achieved.

-- 
With Best Regards,
Andy Shevchenko