RE: [PATCH v1] ARM: tegra: Fix sd4 regulator in Jetson TK1 device tree

[Vidya Sagar]

> -----Original Message-----
> From: Stephen Warren [mailto:swarren@xxxxxxxxxxxxx]
> Sent: Monday, September 29, 2014 9:15 PM
> To: Vidya Sagar
> Cc: thierry.reding@xxxxxxxxx; Laxman Dewangan; Krishna Thota; linux-
> tegra@xxxxxxxxxxxxxxx; linux@xxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v1] ARM: tegra: Fix sd4 regulator in Jetson TK1 device
> tree
> 
> On 09/29/2014 04:25 AM, Vidya Sagar wrote:
> >
> >> -----Original Message-----
> >> From: Stephen Warren [mailto:swarren@xxxxxxxxxxxxx]
> >> Sent: Tuesday, September 23, 2014 12:36 AM
> >> To: Vidya Sagar
> >> Cc: thierry.reding@xxxxxxxxx; Laxman Dewangan; Krishna Thota; linux-
> >> tegra@xxxxxxxxxxxxxxx; linux@xxxxxxxxxxxxxxxx; linux-
> >> kernel@xxxxxxxxxxxxxxx
> >> Subject: Re: [PATCH v1] ARM: tegra: Fix sd4 regulator in Jetson TK1
> >> device tree
> >>
> >> On 09/22/2014 11:57 AM, Vidya Sagar wrote:
> >>> sd4 is an always on regulator which is turned on at boot time.
> >>> It is externally controller through gpio. This change reflects the
> >>> same in Jetson TK1 device tree
> >>
> >> In the schematics, the "Power Sequencing" timing diagram says "S/W
> >> controlled" for SD4/+1.05V_RUN. I also don't see an "ENABLE1" pin on
> >> the AS3722, which would be required for ...
> 
> Can you please comment on this aspect of the issue?
> 
> >>> +					ams,ext-control = <1>;
> >>
> >> ... to be valid.
> >>
> >> What's the source of information behind this change?
> >>
> >> What symptoms does this patch correct?
> >
> > I'm seeing one issue when I add support for PCIe suspend/resume
> functionality.
> > The issue is that, when regulator_bulk_diable() is called, disabling one of
> the power rails (which is deriving its voltage from SD4) of PCIe is failing.
> > The reason being, I2C controller is getting power gated
> 
> Why is the fix being applied to SD4 if the issue is with a power rail derived
> from SD4? Shouldn't any fix be applied directly to the problematic rail rather
> than some parent rail?
> 
> Since the I2C controller is part of the SoC and we don't have power domain
> support yet, the only way the I2C controller can get power gated is when the
> SoC as a whole is turned off.
> 
>  > before power rail disable is called.
> 
> ... so without making SD4 dependant on ext-control, since no SW can be
> running at this point, the only way SD4 could get turned off is that the PMIC
> turns it off itself at the appropriate point in the system power sequence
> based on its OTP programming, or the board HW is already set up to turn off
> SD4 at the appropriate time somehow. Is that not happening?
> That would imply incorrect PMIC programming wouldn't it?
> 

After some debugging, found that the I2C driver's suspend is getting called before the suspend
of PCIe is called (BTW, PCie has suspend_noirq..!) Hence, when PCIe driver wants to disable regulators
it fails because of I2C write failure, which is expected given I2C is already suspended.
Hence, SD4 is made dependent on ENABLE1 input which is the sleep signal from Tegra.

> > Hence SD4 is made dependent on ENABLE1, which is nothing but the deep
> > sleep signal coming from Tegra, So eventually, SD4 will be powered off
> when system enters into deep-sleep state.
> 
> This sounds like a workaround that happens to make the system do what you
> want rather than a root-cause fix.
> 
> > Source of information is from downstream kernel
> 
> We need to use HW schematics and other primary data to determine the
> correct approach.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/