RE: [PATCH 03/19] omap3+: voltage: remove initial voltage

[Vishwanath Sripathy <vishwanath.bs@ti.com>]

> -----Original Message-----
> From: Nishanth Menon [mailto:nm@ti.com]
> Sent: Sunday, February 20, 2011 10:42 AM
> To: Vishwanath Sripathy
> Cc: linux-omap; Tony Lindgren; Kevin Hilman
> Subject: Re: [PATCH 03/19] omap3+: voltage: remove initial voltage
>
> Vishwanath Sripathy wrote, on 02/19/2011 06:54 PM:
> [..]
> >> omap2_set_init_voltage should setup the curr_volt based on which
> OPP
> >> the system is functioning at. Blindly setting a 1.2v setting in the
> >> initial structure may not even match the default voltages stored in
> >> the voltage table which are supported for the domain.
> >>
> >> For example, OMAP3430 core domain does not use 1.2v and ends up
> >> generating a warning on the first transition.
> >>
> [..]
> >> diff --git a/arch/arm/mach-omap2/voltage.c b/arch/arm/mach-
> >> omap2/voltage.c
> >> index 12be525..280ee12 100644
> >> --- a/arch/arm/mach-omap2/voltage.c
> >> +++ b/arch/arm/mach-omap2/voltage.c
> [..]
> >>   	/* Generic voltage parameters */
> >> -	vdd->curr_volt = 1200000;
> > Where do you update this parameter upon initialization? Shouldn't you
> read
> > the VP register and find the actual current voltage and update this
> param?
>
> The sequence is as follows:
> a) omapx_vdd_data configure is called as part of sr init sequence.
> 	And the curr_volt with this patch is not updated at this stage.
> b) somewhere down in the boot sequence, pm.c's
> omap2_set_init_voltage
> starts up. This looks up the current clk frequency from clock layer of
> the parent device for the domain, picks up the nominal voltages stored
> in the opp layer, then does a omap_voltage_scale_vdd to that voltage. In
> omap_voltage_scale_vdd, The current voltage is merely picked off the vp
> (in _pre_volt_scale). the last step it does is to setup vdd->curr_volt.
> This can then be used by dvfs layer etc to make appropriate decisions.
>
> So, No, I dont think I need to update it here, it should happen as part
> of the pm init sequence.
>
> Could you explain what problem do you foresee by doing this?
What if omap_voltage_scale_vdd fails when called from
omap2_set_init_voltage? Or omap2_set_init_voltage returns error even
before calling omap_voltage_scale_vdd because it could not find the
matching voltage for the frequency set by bootloader?

Your assumption that curr_volt is always set by omap2_set_init_voltage
need not be true always.

Vishwa
>
> --
> Regards,
> Nishanth Menon