From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kai Poggensee <kai.poggensee@avionic-design.de>
Date: Fri, 25 May 2012 20:56:09 +0200
Subject: [U-Boot] [PATCH v2 5/7] tegra: Implement gpio_early_init() on
	Tamonten
In-Reply-To: <20120525174003.GC18894@avionic-0098.adnet.avionic-design.de>
References: <1337953588-20696-1-git-send-email-thierry.reding@avionic-design.de>
	<1337953588-20696-5-git-send-email-thierry.reding@avionic-design.de>
	<4FBFB2D6.1040602@wwwdotorg.org>
	<20120525174003.GC18894@avionic-0098.adnet.avionic-design.de>
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Hi Thierry,

On 25.05.2012 19:40, Thierry Reding wrote:
> * 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.

As an aside: A pulse wont be enough in this specific case
as a pull-down on the carrier would lead to the nRST going
low thus resetting the baseboard peripherals.

Plus there is a status LED on the Tamonten Evaluation carrier
that would then indicate the red "system not up".

Cheers,
Kai