[U-Boot] [PATCH v2 5/7] tegra: Implement gpio_early_init() on Tamonten

[Thierry Reding <thierry.reding@avionic-design.de>]

* Stephen Warren wrote:
> On 05/25/2012 07:46 AM, Thierry Reding wrote:
> > The PI4 GPIO is used on Tamonten to reset carrier board peripherals.
> > Power sequencing hardware on the carrier pulls the reset low before
> > powering up the Tegra, and the CPU is supposed to signal readiness,
> > and therefore bring peripherals out of reset by pulling PI4 high.
> 
> > +void gpio_early_init(void)
> > +{
> > +	gpio_request(GPIO_PI4, NULL);
> > +	gpio_direction_output(GPIO_PI4, 1);
> > +	gpio_free(GPIO_PI4);
> > +}
> 
> Do you really mean to free the GPIO here?
> 
> While gpio_free() does not do this at present, it seems perfectly
> reasonable for someone to modify gpio_free() so that instead of leaving
> the HW in some random state when free, it actively reprograms the pin to
> be an input instead, since that's the most conflict-free setting when
> the pin is actively unused.

I believe that even a pulse would be enough for the undelying mechanisms to
take effect, but I'll have to check with our hardware engineers to be sure.
You're probably right, though, that keeping it requested until control is
handed over to the kernel may be safer. I'll update the patch.

Thierry
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