Re: [PATCH v9 1/2] gpio: mmio: add DT support for memory-mapped GPIOs

[Alexandre Courbot <gnurou@xxxxxxxxx>]

On Thu, May 12, 2016 at 9:07 PM, Christian Lamparter
<chunkeey@xxxxxxxxxxxxxx> wrote:
> On Thursday, May 12, 2016 07:26:32 PM Alexandre Courbot wrote:
>> On Wednesday, May 11, 2016 6:34:34 PM JST, Christian Lamparter wrote:
>> > From: Álvaro Fernández Rojas <noltari@xxxxxxxxx>
>> >
>> > This patch adds support for defining memory-mapped GPIOs which
>> > are compatible with the existing gpio-mmio interface. The generic
>> > library provides support for many memory-mapped GPIO controllers
>> > that are found in various on-board FPGA and ASIC solutions that
>> > are used to control board's switches, LEDs, chip-selects,
>> > Ethernet/USB PHY power, etc.
>> >
>> > For setting GPIO's there are three configurations:
>>
>> s/GPIO's/GPIOs
> OK
>
>> >     1. single input/output register resource (named "dat"),
>> >     2. set/clear pair (named "set" and "clr"),
>> >     3. single output register resource and single input resource
>> >        ("set" and dat").
>> >
>> > The configuration is detected by which resources are present.
>> > For the single output register, this drives a 1 by setting a bit
>> > and a zero by clearing a bit.  For the set clr pair, this drives
>> > a 1 by setting a bit in the set register and clears it by setting
>> > a bit in the clear register. The configuration is detected by
>> > which resources are present.
>>
>> The last sentence of this paragraph repeats for first one.
> Ok
>
>> >
>> > For setting the GPIO direction, there are three configurations:
>> >     a. simple bidirectional GPIOs that requires no configuration.
>> >     b. an output direction register (named "dirout")
>> >        where a 1 bit indicates the GPIO is an output.
>> >     c. an input direction register (named "dirin")
>> >        where a 1 bit indicates the GPIO is an input.
>> >
>> > The first user for this binding is "wd,mbl-gpio".
>> >
>> > Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
>> > Signed-off-by: Álvaro Fernández Rojas <noltari@xxxxxxxxx>
>> > Signed-off-by: Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>
>> > ---
>> >  static void bgpio_write8(void __iomem *reg, unsigned long data)
>> >  {
>> > @@ -569,6 +571,58 @@ static void __iomem *bgpio_map(struct
>> > platform_device *pdev,
>> >     return devm_ioremap_resource(&pdev->dev, r);
>> >  }
>> >
>> > +#ifdef CONFIG_OF
>> > +static int bgpio_basic_mmio_parse_dt(struct platform_device *pdev,
>> > +                                struct bgpio_pdata *pdata,
>> > +                                unsigned long *flags)
>> > +{
>> > +   struct device *dev = &pdev->dev;
>> > +
>> > +   pdata->base = -1;
>> > +
>> > +   if (of_property_read_bool(dev->of_node, "no-output"))
>> > +           *flags |= BGPIOF_NO_OUTPUT;
>>
>> I don't think it is a good idea to add "generic" properties. Whether a
>> controller is capable of output or not should be determined by its
>> compatible string only, and not a vague property.
>
> Well, meet the gpios on the MBL. If you want to figure out how WD wired
> up these two GPIOs (one is input, the other output), I can sent you a
> built-yourself MBL kit. It just needs a 3,5" drive and a 12V 2A power
> plug with a standard 5.5mm plug.
>
>> > +
>> > +   return 0;
>> > +}
>> > +
>> > +static const struct of_device_id bgpio_of_match[] = {
>> > +   { .compatible = "wd,mbl-gpio", .data = bgpio_basic_mmio_parse_dt },
>>
>> Mmm cannot you determine whether your controller is capable of output or
>> not just from the compatible property here? If so, the
>> bgpio_basic_mmio_parse_dt seems to be unneeded. If not, then this is
>> dependent on the wd,mbl-gpio binding and should be renamed accordingly.
> Sadly I don't know of any method. The device has two GPIOs one at 0x4e0000000.
> The other one is at 0x4e0100000. The address tells me that there are two
> external chips connected to the EBC (memory bank - RAM, ROM and DMA chips
> go here according to IBM's documentations). Which is not the place you
> would expect peripherals.

Ok, if you have no way of figuring that out then this is legit.

>
>> > @@ -646,6 +709,7 @@ MODULE_DEVICE_TABLE(platform, bgpio_id_table);
>> >  static struct platform_driver bgpio_driver = {
>> >     .driver = {
>> >             .name = "basic-mmio-gpio",
>> > +           .of_match_table = of_match_ptr(bgpio_of_match),
>> >     },
>> >     .id_table = bgpio_id_table,
>> >     .probe = bgpio_pdev_probe,
>>
>> It seems to me that this patch does two things:
>>
>> 1) Add code to support device tree lookup
>> 2) Add support for "wd,mbl-gpio".
>>
>> If true, these two things should be in their own patches. You should also
>> have another patch that adds the DT bindings for "wd,mbl-gpio", so I would
>> do things in that order:
>
> The DT bindings have been merged. That's why I dropped it from the rebase.
>
>> 1/3: DT support for basic-mmio-gpio
> Sadly, adding the "basic-mmio-gpio" binding is not possible without a ACK from
> the device tree maintainers. They have voiced their concerns. I think this was
> your post of the discussion on it:
> <http://www.spinics.net/lists/devicetree/msg124613.html>
>
> That's why the series was updated around v5 and v6 to use the "wd,mbl-gpio"
> binding.
>
> So yes, I wanted to go this route in the beginning as well. But no go.
> If we find more devices we could have a "basic-mmio-gpio" class. But
> for now, we have to start somewhere.

Ah, I was not suggesting that you add a "basic-mmio-gpio" compatible
property, but that the first patch of the series should add the
infrastructure code required for "wd,mbl-gpio" and the drivers you are
moving to use it in 2/2. That way you separate the addition of support
code to the actual device support.

>> 2/3: DT bindings for "wd,mbl-gpio" (and have them validated by the DT
>> people - e.g. do you really need a "reg" property or is it here just to fit
>> with what bgpio_pdev_probe expects? More about this on 2/2)
>> 3/3: Support for "wd,mbl-gpio" in basic-mmio-gpio
> Yes, that would have been nice. And I agree it was the way to do it. But
> without the wd,mbl-gpio mapping I would add the bgpio_parse_dt function
> without any caller. (As I can't add the compatible = "basic-mmio-gpio", ...)

bgpio_parse_dt() is called from bgpio_pdev_probe(), so whether you
have the mapping or not should not matter, does it?

It's just that there is no reason to add support for WD-MBL in this
patch, and convert other drivers in the next - both are equal users of
the infrastructure code you are adding.

Note that my comments on the next patch suggest deeper changes to this
one - you may want to read them as well (I will ignore v9.1 for now).
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