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Message-ID: <20130827103949.GF19893@e106331-lin.cambridge.arm.com>
Date: Tue, 27 Aug 2013 11:39:49 +0100
From: Mark Rutland <mark.rutland@....com>
To: Tomasz Figa <tomasz.figa@...il.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Linus Walleij <linus.walleij@...aro.org>,
"swarren@...dotorg.org" <swarren@...dotorg.org>,
"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
Pawel Moll <Pawel.Moll@....com>,
"galak@...eaurora.org" <galak@...eaurora.org>,
"rob.herring@...xeda.com" <rob.herring@...xeda.com>
Subject: Re: [PATCH v2 3/3] gpio: pcf857x: Add OF support
On Sat, Aug 24, 2013 at 03:13:11PM +0100, Tomasz Figa wrote:
> On Saturday 24 of August 2013 02:54:07 Laurent Pinchart wrote:
> > Hi Tomasz,
> >
> > Thank you for the review.
> >
> > On Saturday 24 August 2013 02:41:59 Tomasz Figa wrote:
> > > On Tuesday 20 of August 2013 01:04:54 Laurent Pinchart wrote:
> > > > Add DT bindings for the pcf857x-compatible chips and parse the
> > > > device
> > > > tree node in the driver.
> > > >
> > > > Signed-off-by: Laurent Pinchart
> > > > <laurent.pinchart+renesas@...asonboard.com> ---
> > > >
> > > > .../devicetree/bindings/gpio/gpio-pcf857x.txt | 71
> > > > +++++++++++++++++ drivers/gpio/gpio-pcf857x.c
> > > > | 57 ++++++++++++++--- 2 files changed, 119 insertions(+), 9
> > > > deletions(-)
> > > >
> > > > create mode 100644
> > > >
> > > > Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> > > > b/Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt new file
> > > > mode
> > > > 100644
> > > > index 0000000..df94462
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> > > > @@ -0,0 +1,71 @@
> >
> > [snip]
> >
> > > > + - pins-initial-state: Bitmask that specifies the initial state of
> > > > + each pin. When a bit is set to zero, the corresponding pin will
> > > > be
> > > > + initialized to the input (pulled-up) state. When the bit is
> > > > set to + one, the pin will be initialized the the low-level
> > > > output state. If + the property is not specified all pins will
> > > > be initialized to the + input state.
> > >
> > > Hmm, do you actually need to know whether those pins are outputs or
> > > inputs before they get used for first time? I believe any driver
> > > using GPIO will call gpio_direction_{in,out}put() before it starts
> > > using the pin, which will initialize the pin to a known state.
> > >
> > > What I'd suggest is making the driver handle this by having a bit mask
> > > that marks states of pins as defined and flagging all pins as
> > > undefined by default. Then any call to gpio_direction_output() or
> > > _input() would mark it as defined and direction of the pin could be
> > > stored in internal driver structures.
> >
> > The problem is that all pins are controlled through a single I2C write.
> > Setting the direction of a pin will set the direction of all other pins.
> > I thus need to know what the initial settings are to avoid glitches.
I guess it's not possible to read the initial state from the hardware?
>
> Oh, that's a funny hardware, isn't it? :)
>
> Well, I guess it can't be helped then. Sorry for the noise.
>
> > > > + The I/O expander can detect input state changes, and thus
> > > > optionally
> > > > + act as an interrupt controller. When interrupts support is
> > > > desired
> > >
> > > I don't like this statement. Device tree should represent what the
> > > device allows you to do, not what you want the device to do.
> > >
> > > My opinion on this is that if the chip supports interrupts then it
> > > should always be an interrupt-controller (unless its interrupt pin is
> > > not wired on the board, but this still conforms to what I wrote
> > > above).
> >
> > I agree. What about the following text then ?
> >
> > The I/O expander can detect input state changes, and thus optionally act
> > as an interrupt controller. When the expander interrupt pin is
> > connected all the following properties must be set. For more
> > information please see the interrupt controller device tree bindings
> > documentation available at
> > Documentation/devicetree/bindings/interrupt-controller/interrupts.txt.
>
> Sounds good.
>
> > > > diff --git a/drivers/gpio/gpio-pcf857x.c
> > > > b/drivers/gpio/gpio-pcf857x.c
> > > > index 070e81f..50a90f1 100644
> > > > --- a/drivers/gpio/gpio-pcf857x.c
> > > > +++ b/drivers/gpio/gpio-pcf857x.c
> >
> > [snip]
> >
> > > > @@ -50,6 +52,27 @@ static const struct i2c_device_id pcf857x_id[] =
> > > > {
> > > >
> > > > };
> > > > MODULE_DEVICE_TABLE(i2c, pcf857x_id);
> > > >
> > > > +#ifdef CONFIG_OF
> > > > +static const struct of_device_id pcf857x_of_table[] = {
> > > > + { .compatible = "nxp,pcf8574", .data = (void *)8 },
> > > > + { .compatible = "nxp,pcf8574a", .data = (void *)8 },
> > > > + { .compatible = "nxp,pca8574", .data = (void *)8 },
> > > > + { .compatible = "nxp,pca9670", .data = (void *)8 },
> > > > + { .compatible = "nxp,pca9672", .data = (void *)8 },
> > > > + { .compatible = "nxp,pca9674", .data = (void *)8 },
> > > > + { .compatible = "nxp,pcf8575", .data = (void *)16 },
> > > > + { .compatible = "nxp,pca8575", .data = (void *)16 },
> > > > + { .compatible = "nxp,pca9671", .data = (void *)16 },
> > > > + { .compatible = "nxp,pca9673", .data = (void *)16 },
> > > > + { .compatible = "nxp,pca9675", .data = (void *)16 },
> > > > + { .compatible = "maxim,max7328", .data = (void *)8 },
> > > > + { .compatible = "maxim,max7329", .data = (void *)8 },
> > > > + { .compatible = "ti,tca9554", .data = (void *)8 },
> > > > + { }
> > > > +};
> > > > +MODULE_DEVICE_TABLE(of, pcf857x_of_table);
> > > > +#endif
> > > > +
> > > >
> > > > /*
> > > >
> > > > * The pcf857x, pca857x, and pca967x chips only expose one read and
> > > > one
> > > > * write register. Writing a "one" bit (to match the reset state)
> > > > lets
> > > >
> > > > @@ -257,14 +280,29 @@ fail:
> > > > static int pcf857x_probe(struct i2c_client *client,
> > > >
> > > > const struct i2c_device_id *id)
> > > >
> > > > {
> > > >
> > > > - struct pcf857x_platform_data *pdata;
> > > > + struct pcf857x_platform_data *pdata = client-
> >dev.platform_data;
> > > > + struct device_node *np = client->dev.of_node;
> > > >
> > > > struct pcf857x *gpio;
> > > >
> > > > + unsigned int n_latch = 0;
> > > > + unsigned int ngpio;
> > > >
> > > > int status;
> > > >
> > > > - pdata = client->dev.platform_data;
> > > > - if (!pdata) {
> > > > +#ifdef CONFIG_OF
> > > > + if (np) {
> > >
> > > Wouldn't if (IS_ENABLED(CONFIG_OF) && np) be sufficient here, without
> > > the #ifdef? You would have to move the match table out of the #ifdef
> > > in this case, though...
> >
> > That's the exact reason why I've used #ifdef CONFIG_OF here, I didn't
> > want to add the overhead of the pcf857x_of_table when CONFIG_OF isn't
> > defined.
>
> I'm not sure if I remember correctly, but I think there was something said
> in one of discussions some time ago, that we should be moving away from
> ifdef'ing such things, in favour of just having them compiled
> unconditionally.
I was also under this impression, but I have no strong feelings either
way.
Thanks,
Mark.
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