Re: [PATCH] arm64: dts: rockchip: Fix the DCDC_REG2 minimum voltage on Quartz64 Model B

["Heiko Stübner" <heiko@sntech.de>]

Am Montag, 3. Juni 2024, 06:51:58 CEST schrieb Dragan Simic:
> On 2024-06-03 06:41, Dragan Simic wrote:
> > On 2024-06-03 05:49, Chen-Yu Tsai wrote:
> >> On Sat, Jun 1, 2024 at 6:41 AM Dragan Simic <dsimic@manjaro.org> 
> >> wrote:
> >>> On 2024-05-31 20:40, Heiko Stübner wrote:
> >>> > Am Freitag, 31. Mai 2024, 00:48:45 CEST schrieb Dragan Simic:
> >>> >> On 2024-05-29 18:27, Chen-Yu Tsai wrote:
> >>> >> > On Tue, May 21, 2024 at 1:20 AM Dragan Simic <dsimic@manjaro.org>
> >>> >> > wrote:
> >>> >> >>
> >>> >> >> Correct the specified regulator-min-microvolt value for the buck
> >>> >> >> DCDC_REG2
> >>> >> >> regulator, which is part of the Rockchip RK809 PMIC, in the Pine64
> >>> >> >> Quartz64
> >>> >> >> Model B board dts.  According to the RK809 datasheet, version 1.01,
> >>> >> >> this
> >>> >> >> regulator is capable of producing voltages as low as 0.5 V on its
> >>> >> >> output,
> >>> >> >> instead of going down to 0.9 V only, which is additionally confirmed
> >>> >> >> by the
> >>> >> >> regulator-min-microvolt values found in the board dts files for the
> >>> >> >> other
> >>> >> >> supported boards that use the same RK809 PMIC.
> >>> >> >>
> >>> >> >> This allows the DVFS to clock the GPU on the Quartz64 Model B below
> >>> >> >> 700 MHz,
> >>> >> >> all the way down to 200 MHz, which saves some power and reduces the
> >>> >> >> amount of
> >>> >> >> generated heat a bit, improving the thermal headroom and possibly
> >>> >> >> improving
> >>> >> >> the bursty CPU and GPU performance on this board.
> >>> >> >>
> >>> >> >> This also eliminates the following warnings in the kernel log:
> >>> >> >>
> >>> >> >>   core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000,
> >>> >> >> not supported by regulator
> >>> >> >>   panfrost fde60000.gpu: _opp_add: OPP not supported by regulators
> >>> >> >> (200000000)
> >>> >> >>   core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000,
> >>> >> >> not supported by regulator
> >>> >> >>   panfrost fde60000.gpu: _opp_add: OPP not supported by regulators
> >>> >> >> (300000000)
> >>> >> >>   core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000,
> >>> >> >> not supported by regulator
> >>> >> >>   panfrost fde60000.gpu: _opp_add: OPP not supported by regulators
> >>> >> >> (400000000)
> >>> >> >>   core: _opp_supported_by_regulators: OPP minuV: 825000 maxuV: 825000,
> >>> >> >> not supported by regulator
> >>> >> >>   panfrost fde60000.gpu: _opp_add: OPP not supported by regulators
> >>> >> >> (600000000)
> >>> >> >>
> >>> >> >> Fixes: dcc8c66bef79 ("arm64: dts: rockchip: add Pine64 Quartz64-B
> >>> >> >> device tree")
> >>> >> >> Cc: stable@vger.kernel.org
> >>> >> >> Reported-By: Diederik de Haas <didi.debian@cknow.org>
> >>> >> >> Signed-off-by: Dragan Simic <dsimic@manjaro.org>
> >>> >> >> ---
> >>> >> >>  arch/arm64/boot/dts/rockchip/rk3566-quartz64-b.dts | 2 +-
> >>> >> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>> >> >>
> >>> >> >> diff --git a/arch/arm64/boot/dts/rockchip/rk3566-quartz64-b.dts
> >>> >> >> b/arch/arm64/boot/dts/rockchip/rk3566-quartz64-b.dts
> >>> >> >> index 26322a358d91..b908ce006c26 100644
> >>> >> >> --- a/arch/arm64/boot/dts/rockchip/rk3566-quartz64-b.dts
> >>> >> >> +++ b/arch/arm64/boot/dts/rockchip/rk3566-quartz64-b.dts
> >>> >> >> @@ -289,7 +289,7 @@ vdd_gpu: DCDC_REG2 {
> >>> >> >>                                 regulator-name = "vdd_gpu";
> >>> >> >>                                 regulator-always-on;
> >>> >> >>                                 regulator-boot-on;
> >>> >> >> -                               regulator-min-microvolt = <900000>;
> >>> >> >> +                               regulator-min-microvolt = <500000>;
> >>> >> >
> >>> >> > The constraints here are supposed to be the constraints of the
> >>> >> > consumer,
> >>> >> > not the provider. The latter is already known by the implementation.
> >>> >> >
> >>> >> > So if the GPU can go down to 0.825V or 0.81V even (based on the
> >>> >> > datasheet),
> >>> >> > this should say the corresponding value. Surely the GPU can't go down
> >>> >> > to
> >>> >> > 0.5V?
> >>> >> >
> >>> >> > Can you send another fix for it?
> >>> >>
> >>> >> I can confirm that the voltage of the power supply of GPU found inside
> >>> >> the RK3566 can be as low as 0.81 V, according to the datasheet, or as
> >>> >> low as 0.825 V, according to the GPU OPPs found in rk356x.dtsi.
> >>> >>
> >>> >> If we want the regulator-min-microvolt parameter to reflect the
> >>> >> contraint
> >>> >> of the GPU as the consumer, which I agree with, we should do that for
> >>> >> other
> >>> >> RK3566-based boards as well, and almost surely for the boards based on
> >>> >> the
> >>> >> RK3568, too.
> >>> >
> >>> > Hmm, I'm not so sure about that.
> >>> >
> >>> > The binding does define:
> >>> >       regulator-min-microvolt:
> >>> >           description: smallest voltage consumers may set
> >>> >
> >>> > This does not seem to describe it as a constraint solely of the
> >>> > consumer.
> >>> > At least the wording sounds way more flexible there.
> >>> >
> >>> > Also any regulator _could_ have multiple consumers, whose value would
> >>> > it need then.
> >>> 
> >>> The way I see it, the regulator-min-microvolt and
> >>> regulator-max-microvolt
> >>> parameters should be configured in a way that protects the 
> >>> consumer(s)
> >>> of the particular voltage regulator against undervoltage and 
> >>> overvoltage
> >>> conditions, which may be useful in some corner cases.
> >>> 
> >>> If there are multiple consumers, which in this case may actually 
> >>> happen
> >>> (IIRC, some boards use the same regulator for the GPU and NPU 
> >>> portions
> >>> of the SoC), the situation becomes far from ideal, because the 
> >>> consumers
> >>> might have different voltage requirements, but that's pretty much an
> >>> unavoidable compromise.
> >> 
> >> As Dragan mentioned, the min/max voltage constraints are there to 
> >> prevent
> >> the implementation from setting a voltage that would make the hardware
> >> inoperable, either temporarily or permanently. So the range set here
> >> should be the intersection of the permitted ranges of all consumers on
> >> that power rail.
> >> 
> >> Now if that intersection happens to be an empty set, then it would up
> >> to the implementation to do proper lock-outs. Hopefully no one designs
> >> such hardware as it's too easy to fry some part of the hardware.
> > 
> > Yes, such a hardware design would need fixing first on the schematic
> > level.  When it comes to the RK3566's GPU and NPU sharing the same
> > regulator, we should be fine because the RK3566 datasheet states that
> > both the GPU and the NPU can go as low as 0.81 V, and their upper
> > absolute ratings are the same at 1.2 V, so 1.0 V, which is as far as
> > the GPU OPPs go, should be fine for both.
> > 
> > As a note, neither the RK3566 datasheet nor the RK3566 hardware design
> > guide specify the recommended upper voltage limit for the GPU or the
> > NPU.  Though, their upper absolute ratings are the same, as already
> > described above.
> 
> Uh-oh, this rabbit hole goes much deeper than expected.  After a quick
> check, I see there are also RK3399-based boards/devices that specify
> the minimum and maximum values for their GPU regulators far outside
> the recommended operating conditions of the RK3399's GPU.
> 
> Perhaps the scope of the upcoming patches should be expanded to cover
> other boards as well, not just those based on the RK356x.
> 
> >>> > While true, setting it to the lowest the regulator can do in the
> >>> > original
> >>> > fix patch, might've been a bit much and a saner value might be better.
> >>> 
> >>> Agreed, but the value was selected according to what the other
> >>> RK3566-based
> >>> boards use, to establish some kind of consistency.  Now, there's a 
> >>> good
> >>> chance for the second pass, so to speak, which should establish 
> >>> another
> >>> different state, but also consistent. :)
> >>> 
> >>> >> This would ensure consistency, but I'd like to know are all those
> >>> >> resulting
> >>> >> patches going to be accepted before starting to prepare them?  There
> >>> >> will
> >>> >> be a whole bunch of small patches.
> >>> >
> >>> > Hmm, though I'd say that would be one patch per soc?
> >>> >
> >>> > I.e. you're setting the min-voltage of _one_ regulator used
> >>> > on each board to a value to support the defined OPPs.
> >>> >
> >>> > I.e. in my mind you'd end up with:
> >>> >       arm64: dts: rockchip: set better min voltage for vdd_gpu on rk356x
> >>> > boards
> >>> >
> >>> > And setting the lower voltage to reach that lower OPP on all affected
> >>> > rk356x boards.
> >>> 
> >>> Yes, the same thoughts have already crossed my mind, but I thought 
> >>> we'd
> >>> like those patches to also include Fixes tags, so they also get
> >>> propagated
> >>> into the long-term kernel versions?  In that case, we'd need one 
> >>> patch
> >>> per
> >>> board, to have a clear relation to the commits referenced in the 
> >>> Fixes
> >>> tags.
> >>> 
> >>> OTOH, if we don't want the patches to be propagated into the 
> >>> long-term
> >>> kernel
> >>> versions, then having one patch per SoC would be perfectly fine.
> >> 
> >> It's really up to Heiko, but personally I don't think it's that 
> >> important
> >> to have them backported. These would be correctness patches, but don't
> >> really affect functionality.
> > 
> > On second thought, I also think that it might be better not to have
> > these changes propagated into the long-term kernel versions.  That
> > would keep the amount of backported changes to the bare minimum, i.e.
> > containing just the really important fixes, while these changes are
> > more on the correctness side.  Maybe together with providing a bit
> > of additional safety.

hehe, up to you I guess :-) .

At least we tied down the how (one patch per soc or so) and not meant
to be backported because more of the correctnes side. So yes I agree with
the arguments for changing the constraints.

Heiko