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Date:   Wed, 29 Apr 2020 14:57:36 +0200
From:   Drew Fustini <drew@beagleboard.org>
To:     Grygorii Strashko <grygorii.strashko@ti.com>
Cc:     =?iso-8859-1?Q?Beno=EEt?= Cousson <bcousson@baylibre.com>,
        Tony Lindgren <tony@atomide.com>,
        Rob Herring <robh+dt@kernel.org>, linux-omap@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jason Kridner <jkridner@beagleboard.org>,
        Robert Nelson <robertcnelson@beagleboard.org>
Subject: Re: [PATCH] arm: dts: am33xx-l4: add gpio-line-names to gpio
 controllers
Message-ID: <20200429125736.GA31476@x1>
References: <20200427233116.GA18917@x1>
 <b15f2577-8a7d-4c18-1633-d47133247f49@ti.com>
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On Tue, Apr 28, 2020 at 10:37:43AM +0300, Grygorii Strashko wrote:
> 
> 
> On 28/04/2020 02:31, Drew Fustini wrote:
> > Add gpio-line-names properties to the gpio controller nodes.  The names
> > correspond to the AM335x pin names which are also the muxmode 0 signal
> > names.  Refer to "Table 4-2. Pin Attributes" in the TI AM335x Sitara
> > Processors datasheet:
> This misuse GPIO DT bindings:
> "
> Optionally, a GPIO controller may have a "gpio-line-names" property. This is
> an array of strings defining the names of the GPIO lines going out of the
> GPIO controller. This name should be the most meaningful producer name
> for the system, such as a rail name indicating the usage. Package names
> such as pin name are discouraged: such lines have opaque names (since they
> are by definition generic purpose) and such names are usually not very
> helpful. For example "MMC-CD", "Red LED Vdd" and "ethernet reset" are
> reasonable line names as they describe what the line is used for. "GPIO0"
> is not a good name to give to a GPIO line. Placeholders are discouraged:
> rather use the "" (blank string) if the use of the GPIO line is undefined
> in your design. The names are assigned starting from line offset 0 from
> left to right from the passed array. An incomplete array (where the number
> of passed named are less than ngpios) will still be used up until the last
> provided valid line index.
> "

Thank you for pointing out that "Package names such as pin name are
discouraged".  That is what I was doing in that patch which I now
realize is incorrect.

The goal to adding the gpio-line-names was to have gpioinfo provide
helpful information to a user on the BeagleBone.  Currently this is all
that appears when booting 5.7-rc2 on a BegaleBone:

debian@beaglebone:~$ gpioinfo
gpiochip0 - 32 lines:
	line   0:      unnamed       unused   input  active-high
	line   1:      unnamed       unused   input  active-high
	line   2:      unnamed       unused   input  active-high
	line   3:      unnamed       unused   input  active-high
	line   4:      unnamed       unused   input  active-high
	line   5:      unnamed       unused   input  active-high
	line   6:      unnamed         "cd"   input   active-low [used]
	line   7:      unnamed       unused   input  active-high
	line   8:      unnamed       unused   input  active-high
	line   9:      unnamed       unused   input  active-high
	line  10:      unnamed       unused   input  active-high
	line  11:      unnamed       unused   input  active-high
	line  12:      unnamed       unused   input  active-high
	line  13:      unnamed       unused   input  active-high
	line  14:      unnamed       unused   input  active-high
	line  15:      unnamed       unused   input  active-high
	line  16:      unnamed       unused   input  active-high
	line  17:      unnamed       unused   input  active-high
	line  18:      unnamed       unused   input  active-high
	line  19:      unnamed       unused   input  active-high
	line  20:      unnamed       unused   input  active-high
	line  21:      unnamed       unused   input  active-high
	line  22:      unnamed       unused   input  active-high
	line  23:      unnamed       unused   input  active-high
	line  24:      unnamed       unused   input  active-high
	line  25:      unnamed       unused   input  active-high
	line  26:      unnamed       unused   input  active-high
	line  27:      unnamed       unused   input  active-high
	line  28:      unnamed       unused   input  active-high
	line  29:      unnamed       unused   input  active-high
	line  30:      unnamed       unused   input  active-high
	line  31:      unnamed       unused   input  active-high
gpiochip1 - 32 lines:
	line   0:      unnamed       unused   input  active-high
	line   1:      unnamed       unused   input  active-high
	line   2:      unnamed       unused   input  active-high
	line   3:      unnamed       unused   input  active-high
	line   4:      unnamed       unused   input  active-high
	line   5:      unnamed       unused   input  active-high
	line   6:      unnamed       unused   input  active-high
	line   7:      unnamed       unused   input  active-high
	line   8:      unnamed       unused   input  active-high
	line   9:      unnamed       unused   input  active-high
	line  10:      unnamed       unused   input  active-high
	line  11:      unnamed       unused   input  active-high
	line  12:      unnamed       unused   input  active-high
	line  13:      unnamed       unused   input  active-high
	line  14:      unnamed       unused   input  active-high
	line  15:      unnamed       unused   input  active-high
	line  16:      unnamed       unused   input  active-high
	line  17:      unnamed       unused   input  active-high
	line  18:      unnamed       unused   input  active-high
	line  19:      unnamed       unused   input  active-high
	line  20:      unnamed       unused   input  active-high
	line  21:      unnamed "beaglebone:green:usr0" output active-high [used]
	line  22:      unnamed "beaglebone:green:usr1" output active-high [used]
	line  23:      unnamed "beaglebone:green:usr2" output active-high [used]
	line  24:      unnamed "beaglebone:green:usr3" output active-high [used]
	line  25:      unnamed       unused   input  active-high
	line  26:      unnamed       unused   input  active-high
	line  27:      unnamed       unused   input  active-high
	line  28:      unnamed       unused   input  active-high
	line  29:      unnamed       unused   input  active-high
	line  30:      unnamed       unused   input  active-high
	line  31:      unnamed       unused   input  active-high
gpiochip2 - 32 lines:
	line   0:      unnamed       unused   input  active-high
	line   1:      unnamed       unused   input  active-high
	line   2:      unnamed       unused   input  active-high
	line   3:      unnamed       unused   input  active-high
	line   4:      unnamed       unused   input  active-high
	line   5:      unnamed       unused   input  active-high
	line   6:      unnamed       unused   input  active-high
	line   7:      unnamed       unused   input  active-high
	line   8:      unnamed       unused   input  active-high
	line   9:      unnamed       unused   input  active-high
	line  10:      unnamed       unused   input  active-high
	line  11:      unnamed       unused   input  active-high
	line  12:      unnamed       unused   input  active-high
	line  13:      unnamed       unused   input  active-high
	line  14:      unnamed       unused   input  active-high
	line  15:      unnamed       unused   input  active-high
	line  16:      unnamed       unused   input  active-high
	line  17:      unnamed       unused   input  active-high
	line  18:      unnamed       unused   input  active-high
	line  19:      unnamed       unused   input  active-high
	line  20:      unnamed       unused   input  active-high
	line  21:      unnamed       unused   input  active-high
	line  22:      unnamed       unused   input  active-high
	line  23:      unnamed       unused   input  active-high
	line  24:      unnamed       unused   input  active-high
	line  25:      unnamed       unused   input  active-high
	line  26:      unnamed       unused   input  active-high
	line  27:      unnamed       unused   input  active-high
	line  28:      unnamed       unused   input  active-high
	line  29:      unnamed       unused   input  active-high
	line  30:      unnamed       unused   input  active-high
	line  31:      unnamed       unused   input  active-high
gpiochip3 - 32 lines:
	line   0:      unnamed       unused   input  active-high
	line   1:      unnamed       unused   input  active-high
	line   2:      unnamed       unused   input  active-high
	line   3:      unnamed       unused   input  active-high
	line   4:      unnamed       unused   input  active-high
	line   5:      unnamed       unused   input  active-high
	line   6:      unnamed       unused   input  active-high
	line   7:      unnamed       unused   input  active-high
	line   8:      unnamed       unused   input  active-high
	line   9:      unnamed       unused   input  active-high
	line  10:      unnamed       unused   input  active-high
	line  11:      unnamed       unused   input  active-high
	line  12:      unnamed       unused   input  active-high
	line  13:      unnamed       unused   input  active-high
	line  14:      unnamed       unused   input  active-high
	line  15:      unnamed       unused   input  active-high
	line  16:      unnamed       unused   input  active-high
	line  17:      unnamed       unused   input  active-high
	line  18:      unnamed       unused   input  active-high
	line  19:      unnamed       unused   input  active-high
	line  20:      unnamed       unused   input  active-high
	line  21:      unnamed       unused   input  active-high
	line  22:      unnamed       unused   input  active-high
	line  23:      unnamed       unused   input  active-high
	line  24:      unnamed       unused   input  active-high
	line  25:      unnamed       unused   input  active-high
	line  26:      unnamed       unused   input  active-high
	line  27:      unnamed       unused   input  active-high
	line  28:      unnamed       unused   input  active-high
	line  29:      unnamed       unused   input  active-high
	line  30:      unnamed       unused   input  active-high
	line  31:      unnamed       unused   input  active-high

I discussed it with Robert Nelson and Jason Kridner and the idea came up
that using the beagle pin header labels would be more useful than the
AM3358 pin names.

> Additional note. On other TI SoCs like am437x the same gpio line can be routed to more
> than one pin (but only one pin can be used).
> gpio0_0 GPIO IO -> A17, D16

Thank you for that insights.

Instead of am33xx-l4.dtsi, I am thinking of adding a gpio-line-names
property in: source/arch/arm/boot/dts/am335x-bone-common.dtsi

For gpiochip0, line 0 and line 1 would be "" as they are not connected
to P8/P9 header.  line 2 would be labeled "P9_22", line 3 would be
"P9_21", etc.  I'll post a complete patch for am335x-bone-common.dtsi
and the gpioinfo output to demonstrate the usefulness.


thanks,
drew