On Fri, Jan 03, 2014 at 10:23:50AM -0800, Dmitry Torokhov wrote:
> On Fri, Jan 03, 2014 at 06:36:05PM +0100, Maxime Ripard wrote:
> > On Thu, Jan 02, 2014 at 11:36:33PM +0100, Hans de Goede wrote:
> > > Hi,
> > >
> > > On 01/02/2014 09:20 PM, Maxime Ripard wrote:
> > > >On Thu, Jan 02, 2014 at 02:45:29PM +0100, Hans de Goede wrote:
> > > >>>Also, instead of inventing yet another vendor-specific property, why
> > > >>>not re-use
> > > >>>a button binding similar to gpio-keys like:
> > > >>>
> > > >>> lradc: lradc@01c22800 {
> > > >>> compatible = "allwinner,sun4i-lradc-keys";
> > > >>> reg = <0x01c22800 0x100>;
> > > >>> interrupts = <31>;
> > > >>> allwinner,chan0-step = <200>;
> > > >>>
> > > >>> #address-cells = <1>;
> > > >>> #size-cells = <0>;
> > > >>>
> > > >>> button@0 {
> > > >>> reg = <0>; /* your channel index from above */
> > > >>> linux,code = <115>; /* already used as
> > > >>> dt-property */
> > > >>> };
> > > >>>
> > > >>> button@1 {
> > > >>> reg = <1>;
> > > >>> linux,code = <114>;
> > > >>> };
> > > >>
> > > >>Ugh no. Having a vendor specific property which is KISS certainly
> > > >>beats this, both wrt ease of writing dts files as well as wrt the
> > > >>dts parsing code in the driver.
> > > >
> > > >I'd agree with Heiko here. This is pretty much the same construct
> > > >that's already in use in other input drivers, like gpio-keys.
> > >
> > > In the gpio case there is a 1 on 1 relation between a single hw
> > > entity (the gpio-pin) and a single keycode. Here there is 1 hw entity
> > > which maps to an array of key-codes, certainly using an array rather
> > > then a much more complicated construct is the correct data-structure
> > > to represent this.
> >
> > You can build an array in your driver out of this very easily, it's 10
> > lines in your probe. And you gain from this something that is more
> > generic, can be shared by other similar drivers and is consistent with
> > what is already in use.
>
> How will it be shared? Surely not code-wise, but basically in spirit
> only. It seems to me that the originally proposed binding is simple and
> concise and works well for the driver.See Heiko's answer, but I do believe the code can be shared as well if needs be. > > > >This is also something that can really easily be made generic, > > > >since this is something that is rather common. > > > > > > > >Speaking of which. I believe this should actually come in two > > > >different drivers: > > > > - The ADC driver itself, using IIO > > > > - A generic button handler driver on top of IIO. > > > > > > > > The fact that on most board this adc is used for buttons doesn't make > > > > any difference, it's actually a hardware designer choice, we should > > > > support that choice, but we should also be able to use it just as an > > > > ADC. > > > > > > No, this is not a generic adc, as mentioned in the commit msg, this > > > adc is specifically designed to be used this way. > > > > > > The adc won't start sampling data, and won't generate any interrupts > > > until a button is pressed. That is until the input voltage drops below > > > 2/3 of Vref, this is checked through a built-in analog comparator, which > > > hooks into the control logic. > > > > > > It has button down and button up interrupts, and can detect long > > > presses (unused) and generate a second type of down interrupt for those. > > > > > > This really is an input device, which happens to use an adc. > > > > Hmm, yes, ok. > > > > > >Carlo Caione already started to work on an IIO driver for the LRADC: > > > >https://github.com/carlocaione/linux/tree/sunxi-lradc > > > >maybe you can take over his work. > > > > > > That won't work because the adc won't sample if the input gets above > > > 2/3 of Vref. There may be some other mode which does not do that, but > > > that is not clearly documented. > > > > > > Even if an IIO driver turns out to be doable, I strongly believe that > > > having a separate input driver for this is best, since this device > > > was designed to be used as such. Building input on top of IIO would > > > mean polling the adc, while with my driver it actually generates > > > button down / up interrupts without any polling being involved. > > > > Not really. iio_channel_read calls the read_raw function (in that > > case) of your driver. If the read_raw function in your driver wants to > > poll the device, fine, but most of the time, it will just block > > waiting for an interrupt to come and return the data to the caller, > > which is obviously the saner behaviour, and you don't actually end up > > polling the device. Which is pretty much the architecture you're using > > already, just with an intermediate layer in between. > > What is the benefit of the IIO layer if device can't really be used as > IIO? I am all for moving as many generic devices as we can to IIO but we > should recognize that sometimes the device is not an IIO device. Yes, I've agreed to that. I was just clarifying Hans' statement. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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