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Date:   Thu, 1 Apr 2021 12:44:15 +0200
From:   Henning Schild <henning.schild@siemens.com>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux LED Subsystem <linux-leds@vger.kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        linux-watchdog@vger.kernel.org,
        Srikanth Krishnakar <skrishnakar@gmail.com>,
        Jan Kiszka <jan.kiszka@siemens.com>,
        Gerd Haeussler <gerd.haeussler.ext@siemens.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Mark Gross <mgross@linux.intel.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Pavel Machek <pavel@ucw.cz>, Enrico Weigelt <lkml@metux.net>
Subject: Re: [PATCH v3 2/4] leds: simatic-ipc-leds: add new driver for
 Siemens Industial PCs
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Am Wed, 31 Mar 2021 18:40:23 +0300
schrieb Andy Shevchenko <andy.shevchenko@gmail.com>:

> On Tue, Mar 30, 2021 at 6:33 PM Henning Schild
> <henning.schild@siemens.com> wrote:
> > Am Tue, 30 Mar 2021 15:41:53 +0300
> > schrieb Andy Shevchenko <andy.shevchenko@gmail.com>:  
> > > On Tue, Mar 30, 2021 at 3:35 PM Henning Schild
> > > <henning.schild@siemens.com> wrote:  
> > > > Am Tue, 30 Mar 2021 15:15:16 +0300
> > > > schrieb Andy Shevchenko <andy.shevchenko@gmail.com>:  
> > > > > On Tue, Mar 30, 2021 at 2:58 PM Henning Schild
> > > > > <henning.schild@siemens.com> wrote:  
> > > > > > Am Tue, 30 Mar 2021 14:04:35 +0300
> > > > > > schrieb Andy Shevchenko <andy.shevchenko@gmail.com>:  
> > > > > > > On Mon, Mar 29, 2021 at 8:59 PM Henning Schild
> > > > > > > <henning.schild@siemens.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.  
> 
> If you remember, I asked you about the chip twice :-)
> I assumed that we were talking about Apollo Lake and that's why I
> insisted that the driver is in the kernel source tree.

Sorry, maybe i did not get the context of your question and which of
the machines you asked about. Now it is clear i guess.

> 
> > > 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.  
> 
> OK!
> 
> > I guess that will still mean the PIO-based part of the LED driver
> > will have to stay as is.  
> 
> Probably yes. I haven't looked into that part and I have no idea
> what's going on on that platform(s).
> 

Which i guess means the series can be reviewed as if the mmio bits for
that apollo lake would not be in it, maybe i will even send a version
without that one box. We have others in the "backlog" might as well
delay that one if it helps sorting out a base-line.

regards,
Henning