On 2024-06-03 06:41, Dragan Simic wrote:

On 2024-06-03 05:49, Chen-Yu Tsai wrote:

quoted

On Sat, Jun 1, 2024 at 6:41 AM Dragan Simic [off-list ref] 
wrote:

quoted

On 2024-05-31 20:40, Heiko Stübner wrote:

quoted

Am Freitag, 31. Mai 2024, 00:48:45 CEST schrieb Dragan Simic:

quoted

On 2024-05-29 18:27, Chen-Yu Tsai wrote:

quoted

On Tue, May 21, 2024 at 1:20 AM Dragan Simic [off-list ref]
wrote:

quoted

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 <redacted>
Signed-off-by: Dragan Simic <redacted>
---
 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.

quoted

quoted

quoted

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. :)

quoted

quoted

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.

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