linux-kernel - Re: [rtc-linux] [PATCH 8/8] ARM: vt8500: gpio: Devicetree support for arch-vt8500

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Date:	Wed, 8 Aug 2012 09:19:52 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	vt8500-wm8505-linux-kernel@...glegroups.com,
	Tony Prisk <linux@...sktech.co.nz>,
	Russell King <linux@....linux.org.uk>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Alan Cox <alan@...ux.intel.com>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Hauke Mehrtens <hauke@...ke-m.de>, Felipe Balbi <balbi@...com>,
	Neil Zhang <zhangwm@...vell.com>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Rob Landley <rob@...dley.net>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Warren <swarren@...dia.com>,
	Eric Andersson <eric.andersson@...xphere.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-fbdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-serial@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [rtc-linux] [PATCH 8/8] ARM: vt8500: gpio: Devicetree support for arch-vt8500

On Wednesday 08 August 2012, Linus Walleij wrote:
> On Wed, Aug 8, 2012 at 3:39 AM, Tony Prisk <linux@...sktech.co.nz> wrote:
> 
> > Converted the existing arch-vt8500 gpio to a platform_device.
> > Added support for WM8505 and WM8650 GPIO controllers.
> (...)
> > +++ b/drivers/gpio/gpio-vt8500.c
> 
> This driver looks very one-bit-per-gpio typed. Are you sure you cannot
> just reuse drivers/gpio/gpio-generic.c? Make a compelling case please...
> 
> > +struct vt8500_gpio_bank_regs {
> > +       int     en;
> > +       int     dir;
> > +       int     data_out;
> > +       int     data_in;
> 
> Why are all these members int? They should be u8 from reading your code.
> 
> > +       int     ngpio;
> > +};

Not necessarily 8 bit, but definitely unsigned.

> > +static struct vt8500_gpio_data vt8500_data = {
> > +       .num_banks      = 7,
> > +       .banks  = {
> > +               VT8500_BANK(0x00, 0x20, 0x40, 0x60, 26),
> > +               VT8500_BANK(0x04, 0x24, 0x44, 0x64, 28),
> > +               VT8500_BANK(0x08, 0x28, 0x48, 0x68, 31),
> > +               VT8500_BANK(0x0C, 0x2C, 0x4C, 0x6C, 19),
> > +               VT8500_BANK(0x10, 0x30, 0x50, 0x70, 19),
> > +               VT8500_BANK(0x14, 0x34, 0x54, 0x74, 23),
> > +               VT8500_BANK(-1, 0x3C, 0x5C, 0x7C, 9),    /* external gpio */
> 
> What on earth are all those magic numbers?
> 
> I *guess* they're enabling some default GPIO settings etc.

No, they are the register offsets you quoted above, per bank. There
is no easy way to abstract these, and I suggested putting the
values into the source code rather than describing each bank
separately in the .dtsi file.

My feeling however is that the "vt8500_chip->regoff" is wrong, which
would mean only the first bank works. The code adds the same offsets
per bank once more that it sets in this bank table.

	Arnd
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