On Wed, 6 Feb 2013 10:31:04 +0100, Lars Poeschel <poeschel@xxxxxxxxxxx> wrote: > On Tuesday 05 February 2013 at 15:29:09, Grant Likely wrote: > > On Thu, 31 Jan 2013 21:51:36 +0100, Linus Walleij > <linus.walleij@xxxxxxxxxx> wrote: > > > On Thu, Jan 31, 2013 at 4:58 PM, Lars Poeschel <larsi@xxxxxxxxxxxxxxxxx> > wrote: > > > > --- /dev/null > > > > +++ b/Documentation/devicetree/bindings/gpio/gpio-mcp23s08.txt > > > > @@ -0,0 +1,27 @@ > > > > +Microchip MCP2308/MCP23S08/MCP23017/MCP23S17 driver for > > > > +8-/16-bit I/O expander with serial interface (I2C/SPI) > > > > + > > > > +Required properties: > > > > +- compatible : Should be "mcp,mcp23s08-gpio", "mcp,mcp23s17-gpio", > > > > + "mcp,mcp23008-gpio" or "mcp,mcp23017-gpio" > > > > +- base : The first gpio number that should be assigned by this chip. > > > > > > No. We do not tie the global GPIO numbers into the device tree. > > > > > > In the DT GPIOs are referenced by ampersand <&gpio0 1 2> > > > notation referring to the instance, so as you realize DT itself > > > has no need for that number. > > > > > > Further it is not OS-neutral. > > > > > > You have to find another way to handle this in the driver code. > > > In worst case: use AUXDATA. > > > > Hi Lars, > > > > The trick is to declare the io expander to be a "gpio-controller" and > > use the #gpio-cells property to declare how many cells (32-bit numbers) > > are need to specify a single gpio line. Most gpio controllers use > > "gpio-cells=<2>"; The first cell is the *controller local* gpio > > number, and the second cell is used for flags. That way your gpio > > controller can be referenced by other nodes in the tree with a "gpios" > > property. > > > > You can find lots of examples of this in the tree. > > Linus, Grant, thanks for the explanations. I think I have catched where it > should go. > The thing that confused me was, that the platform_data for the chip has a > mandatory "base" member, that sets the linux global gpio number at which the > chip should appear. A value of -1 for automatic assigning gpio number is not > allowed, the chip will not probe. > I have to change the driver to allow at least this -1 as an additional value. > As Linus pointed out, it is not desirable to set the global gpio base number > from device tree, right ? If I have 3 instances of this chips then, how can > userspace sw distinguish then to which one it is talking ? You look in sysfs to find the chip you are interested in. That is the place to find out how dynamic numbers have been assigned. g. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
