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 17:23:05 +0200
From:   Henning Schild <henning.schild@...mens.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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

Am Tue, 30 Mar 2021 15:41:53 +0300
schrieb Andy Shevchenko <andy.shevchenko@...il.com>:

> 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.

Ok, so there is the existing driver i asked about several times. Thanks
for pointing it out.

> 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.

Will have a look. Unfortunately this one box is missing in my personal
collection, but let us assume that one can be converted to that
existing driver.
I guess that will still mean the PIO-based part of the LED driver will
have to stay as is.

regards,
Henning