Hi Stephen, On Mon, Dec 5, 2011 at 3:03 PM, Stephen Warren <swar...@nvidia.com> wrote: > On 12/05/2011 03:52 PM, Simon Glass wrote: >> Hi Stephen, >> >> On Mon, Dec 5, 2011 at 2:22 PM, Stephen Warren <swar...@nvidia.com> wrote: >>> On 12/05/2011 02:56 PM, Simon Glass wrote: >>>> Hi Stephen, >>>> >>>> On Mon, Dec 5, 2011 at 1:46 PM, Stephen Warren <swar...@nvidia.com> wrote: >>>>> On 12/02/2011 07:11 PM, Simon Glass wrote: >>>>>> This adds some support into fdtdec for reading GPIO definitions from >>>>>> the fdt. We permit up to FDT_GPIO_MAX GPIOs in the system. Each GPIO >>>>>> is of the form: >>>>>> >>>>>> gpio-function-name = <phandle gpio_num flags>; >>>>>> >>>>>> where: >>>>>> >>>>>> phandle is a pointer to the GPIO node >>>>>> gpio_num is the number of the GPIO (0 to 223) >>>>>> flags is some flags, proposed as follows: >>>>>> >>>>>> bit meaning >>>>>> 0 0=input, 1=output >>>>>> 1 for output only: inital value of output >>>>>> 2 0=polarity normal, 1=active low (inverted) >>>>> >>>>> The meaning of the flags (and even whether there are any flags any if so >>>>> how many cells there are to contain them) is defined by the GPIO >>>>> controller's binding. It's not something that can be interpreted in >>>>> isolation by a generic DT parsing function. See for example #gpio-cells >>>>> in tegra20.dtsi's gpio node and kernel file >>>>> Documentation/devicetree/bindings/gpio/gpio_nvidia.txt. >>>> >>>> I see this in my version: >>>> >>>> Required properties: >>>> - compatible : "nvidia,tegra20-gpio" >>>> - #gpio-cells : Should be two. The first cell is the pin number and the >>>> second cell is used to specify optional parameters: >>>> - bit 0 specifies polarity (0 for normal, 1 for inverted) >>>> - gpio-controller : Marks the device node as a GPIO controller. >>>> >>>> so how do I go about adding the other two bits? >>> >>> I don't think you would. Input vs. output and output value are set up by >>> APIs such as gpio_direction_input/output based on what the driver wants >>> to do with the GPIOs. >> >> Fair enough. I am wanting to create a way for more information to be >> provided about a GPIO so that it can be set up automatically ready for >> use (reduces code size). > > At least in this case, I don't think it makes sense to do that. The FDT > is about representing that a particular GPIO is a VBUS GPIO. That > doesn't mean the GPIO /has/ to be an output driven high; that's only > true if the driver is enabled and chooses to configure that port as a > host port, not a device port. > > If you wanted to represent GPIOs that were always configured to a > specific output value in DT, I think that'd be an unrelated binding > somewhere other than the USB bus's vbus-gpios property, since it'd have > a completely different semantic meaning.
I feel that it is useful to have a generic gpio setup function which can at least set gpio to input or output. We could even make it optional with an additional flag. IMO a lot of the reason for only having one flag is that no one can OR together two decimal numbers (i.e. we need symbolic constants in the fdt). But for now I will drop this comment and the fdtdec_setup_gpio() function. This will increase code size slightly since every driver will need to call gpio_direction_input/output() manually. > >>> include/asm-generic/gpio.h seems to use an int to represent a GPIO. I'd >>> suggest these APIs do the same, rather than use a u8. >> >> Do you mean the fdt_gpio_state structure? > > Yes. > >> I have not used u8 for any >> function calls and would not. >> >> This adds 3 bytes for every entry. What is the benefit? People get >> upset when we waste memory! > > Well, U-boot has already chosen to use an int to represent a GPIO ID. > Given that, I assert that all places that store a GPIO ID should use the > same type. And realistically, we're only talking about a handful of > instances here, and any bloat is completely limited to those platforms > that use this feature, and linear with the number of GPIOs. OK I have changed this. Each structure element is now 4 bytes (50%) bigger than before but I don't think this will add up to more than a few hundred bytes all up. Regards, Simon > > -- > nvpublic _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
