On Mon 25 Oct 13:17 PDT 2021, Stephen Boyd wrote:

Quoting Bjorn Andersson (2021-10-25 12:10:35)

quoted

On Mon 25 Oct 02:07 PDT 2021, Sandeep Maheswaram wrote:

quoted

Add multi pd bindings to set performance state for cx domain
to maintain minimum corner voltage for USB clocks.

Signed-off-by: Sandeep Maheswaram <redacted>
---
v2:
Make cx domain mandatory.

 Documentation/devicetree/bindings/usb/qcom,dwc3.yaml | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml b/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml
index 2bdaba0..fd595a8 100644
--- a/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml
+++ b/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml

@@ -42,7 +42,13 @@ properties:

   power-domains:
     description: specifies a phandle to PM domain provider node
-    maxItems: 1
+    minItems: 2
+    items:
+      - description: cx power domain
+      - description: USB gdsc power domain
+
+  required-opps:
+    description: specifies the performance state to power domain

I'm still worried about the fact that we can't just rely on the USB GDSC
being a subdomin of CX in order to just "turn on" CX.

Afaict accepting this path forward means that for any device that sits
in a GDSC power domain we will have to replicate this series for the
related driver.

I suspect the problem is that it's not just "turn on" but wanting to
turn it on and then set the performance state to some value based on the
clk frequency.

I don't see an opp-table involved, just the required-opps for the
purpose of turning CX on a little bit more. Perhaps I'm missing
something here though.

Maybe the simplest version of that could be supported
somehow by having dev_pm_opp_set_rate() figure out that the 'level'
applies to the parent power domain instead of the child one?

Having the performance_state request cascade up through the GDSC sounds
like a nice solution; I've not looked at the code to see if this is
feasible though.

Or we may need to make another part of the OPP binding to indicate the
relationship between the power domain and the OPP and the parent of
the power domain.

I suspect this would be useful if a power-domain provider needs to
translate a performance_state into a different supply-performance_state.
Not sure if we have such case currently; these examples are all an
adjustable power-domain with "gating" subdomains.


PS. I think we have the same problem in the display subsystem, the
sub-blocks are powered by MDSS_GDSC, which is a subdomain of MMCX. We
trust the parent mdss node to keep the GDSC powered and specify MMCX as
the power-domain for the children, so that we can affect their levels by
respective opp-table.

Regards,
Bjorn