linux-kernel - Re: [PATCH 1/3] GPIO: gpio-dwapb: Enable platform driver binding to MFD driver

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Date:	Thu, 4 Sep 2014 12:01:22 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	"Chen, Alvin" <alvin.chen@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"sebastian@...akpoint.cc" <sebastian@...akpoint.cc>,
	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	"gnurou@...il.com" <gnurou@...il.com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"dvhart@...ux.intel.com" <dvhart@...ux.intel.com>
Subject: Re: [PATCH 1/3] GPIO: gpio-dwapb: Enable platform driver binding to
 MFD driver

On Thu, 2014-09-04 at 10:38 +0000, Chen, Alvin wrote:
> 
> > > Since we enable this module not only support OF devices, but also support
> > MFD devices, so we remove OF_GPIO dependenc
> > > For 'PCI', the original code is also not depended on PCI, and this patch also
> > not, do you think it is necessary?
> > 
> > if not PCI then you should add something likwe
> > 	"depends on OF_GPIO || MFD"
> > 
> > looking further, you need also HAS_IOMEM for things like
> > devm_ioremap_resource(). Linus, wouldn't it make sense to group this driver
> > and make the block depend on it?
> > 
> I can add "depends on OF_GPIO || INTEL_QUARK_I2C_GPIO_MFD", since now the MFD path only support Intel Quark.
> 
> Andriy, how do you think?

I think we don't need that dependency at all since OF_GPIO has stubs for
non-OF case. Am I missing something?

GPIOLIB dependency is implied in Kconfig, by the way.

P.S. See, for example, leds-gpio.c

> 
> > > > >  struct dwapb_gpio {
> > > > >  	struct	device		*dev;
> > > > >  	void __iomem		*regs;
> > > > >  	struct dwapb_gpio_port	*ports;
> > > > > -	unsigned int		nr_ports;
> > > > you could keep this the way it is
> > > It has been moved to 'pdata'.
> > 
> > I saw that. But there is no need keep a pointer to pdata across the whole driver
> > since only need nr_ports in the driver removal part of the whole driver.
> Got your idea. So can I just use a global static pdata pointer instead of adding it as a member of ' struct dwapb_gpio'?
> Since pdata is used in all 'probe' functions, and make pdata as global static make programming more easy.
> 
> > 
> > > > >  	struct irq_domain	*domain;
> > > > > +	const struct dwapb_gpio_platform_data	*pdata;
> > > >
> > > > and not making this a member of this struct. I've been going up and
> > > > down the source and I don't see the need to marry dwapb_gpio to
> > > > dwapb_gpio_platform_data.
> > > > That dwapb_gpio_port_property thing has a long name. Could you just
> > > > set it up, pass it for registration and the free it? You can't free
> > > > the pdata for the non-OF tree but for the OF case you keep that struct
> > around for no reason.
> > > > You could safe some memory and use pdata directly for setup.
> > > Here, 'pdata' is used for both OF and MFD. For MFD, 'pdata' is passed from
> > MFD.
> > > For OF, 'pdata' is getting from device nodes properties. Why do we
> > > have such design? Because it can make the handling more easy for
> > > flowing routine. All necessary properties get from 'pdata', never care it is
> > from OF or MFD. And someone are working on replacing OF interface with a
> > firmware agnostic device_property* interface which will work with both OF and
> > ACPI.
> > > More information for this design, please contact Darren Hart
> > <dvhart@...ux.intel.com>. Darren Hart wrote to me:
> > > "Generally speaking, rather than if/else blocks throughout the code
> > > checking if it is enumerated via open firmware or as a platform device, a
> > cleaner approach is to check if the pdata is null, and if so, populate the pdata
> > from the open firmware description if present.
> > > Then use the pdata throughout the driver.
> > 
> > But isn't it enough to hold on to this pdata thing through the probe function
> > only? After probe is done you could drop that memory in the OF-case, right?
> OK. If it is OF-case, pdata can be freed in the end of probe.
> 
> 
> > > > > +	irq_set_handler_data(port->pp->irq, gpio);
> > > >
> > > > This does not look like it belongs here. It should only be used
> > > > together with
> > > > irq_set_chained_handler() or am I missing here something?
> > > This patch reused ' dwapb_irq_handler', it needs the irq handler data. For '
> > irq_set_handler_data', it just sets the irq data.
> > > Why do you think it must be used together with ' irq_set_chained_handler'?
> > 
> > because you do request_irq(…, driver_data). If you you look close to
> > irq_set_chained_handler() it does not have such a member. Thus it uses
> > irq_set_handler_data() for that same purpose.
> > 
> OK. I can improve it.


-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy
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