Hi,
On Sun, Dec 23, 2012 at 08:58:13PM +0000, Paul Walmsley wrote:
> > In this specific case the pin is connected to nCONFIG of a FPGA. The
> > FPGA is commanded to start configuration from a SPI flash in the
> > bootloader, so it can happen in parallel with kernel
> > load/uncompress/startup, but as the kernel resets the gpio during
> > initialization this doesn't work.
> >
> > Digging a bit into it, I see the hwmod of the gpio controller is
> > configured to reset at startup, and it works correctly (E.G. the pin is
> > left asserted) if I change it to HWMOD_INIT_NO_RESET:
> >
> > --- a/arch/arm/mach-omap2/omap_hwmod_33xx_data.c
> > +++ b/arch/arm/mach-omap2/omap_hwmod_33xx_data.c
> > @@ -992,7 +992,7 @@ static struct omap_hwmod am33xx_gpio1_hwmod = {
> > .name = "gpio2",
> > .class = &am33xx_gpio_hwmod_class,
> > .clkdm_name = "l4ls_clkdm",
> > - .flags = HWMOD_CONTROL_OPT_CLKS_IN_RESET,
> > + .flags = (HWMOD_INIT_NO_IDLE | HWMOD_INIT_NO_RESET),
> > .mpu_irqs = am33xx_gpio1_irqs,
> > .main_clk = "l4ls_gclk",
> > .prcm = {
> >
> > Now the question is why is this configured like this?
>
> This behavior is intended to decouple the kernel from the bootloader, or
> previously-booted operating system (e.g., the kexec case). The original
> goal was to place the system in an known safe state as soon as possible
> after the kernel starts. This is to prevent misconfigured or
there is one "issue" with this. At least on AM335x starter kit, GPIO0_7
is used as DDR power pin. If we reset that GPIO bank, DDR looses power
and "for obscure reasons" (:-)) the board doesn't boot.
In this case, we cannot reset that bank, otherwise Starter Kit will
never boot in mainline. Bad PCB design, I know, but it's not something
we can change now :-)
cheers
--
balbi
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