Re: [PATCH 1/2] gpio: Add a driver for Cadence GPIO controller

[Simon Hatliff]

Hi Boris, Linus,

On 30/03/17 12:29, Boris Brezillon wrote:
> Hi Linus,
>
> On Thu, 30 Mar 2017 11:03:45 +0200
> Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
>
> > On Wed, Mar 29, 2017 at 6:04 PM, Boris Brezillon
> > <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > Add a driver for Cadence GPIO controller.
> > IIUC Cadence do a lot of things. Are there variants of this controller?
> I'll let Simon answer that one.
This is a controller that has been around since 2000.  It is not 
configurable in any way, so there are no variants.  Cadence do not offer 
any other GPIO controllers as IP.
> > > +static irqreturn_t cdns_gpio_irq_handler(int irq, void *dev)
> > > +{
> > > +       struct cdns_gpio_chip *cgpio = dev;
> > > +       unsigned long status;
> > > +       int hwirq;
> > > +
> > > +       /*
> > > +        * FIXME: If we have an edge irq that is masked we might lose it
> > > +        * since reading the STATUS register clears all IRQ flags.
> > > +        * We could store the status of all masked IRQ in the cdns_gpio_chip
> > > +        * struct but we then have no way to re-trigger the interrupt when
> > > +        * it is unmasked.
> > > +        */
> > It is marked FIXME but do you think it can even be fixed? It seems
> > like a hardware flaw. :(
> Maybe not. Unless Simon comes up with a magic register to re-trigger an
> interrupt :-).
There are no plans to update the controller.
> Another solution would be to write 0xffffffff into CDNS_GPIO_OUTPUT_EN
> at probe time so that each time CDNS_GPIO_DIRECTION_MODE is modified to
> set a pin in output mode, the CDNS_GPIO_OUTPUT_EN is already correctly
> configured.
> Simon, would that work? Is there a good reason to keep a bit in
> CDNS_GPIO_OUTPUT_EN set to 0 when the GPIO is in input mode (power
> consumption?)?
If direction_mode is set to input then output_en is ignored so this 
should work.  The hardware defaults to output mode, so as long as you 
set all pins to input mode before you set all output_en bits there 
should be no negative effect.

Cheers,
-- Simon