Re: [RFC 3/7] mfd: devicetree: bindings: Add Qualcomm SMD based RPM DT binding

From: Jeffrey Hugo
Date: Wed Oct 08 2014 - 17:47:15 EST

On 9/30/2014 6:08 PM, Bjorn Andersson wrote:
On Tue 30 Sep 16:16 PDT 2014, Jeffrey Hugo wrote:

On 9/30/2014 8:37 AM, Bjorn Andersson wrote:
On Tue 30 Sep 06:46 PDT 2014, Kumar Gala wrote:


On Sep 29, 2014, at 7:34 PM, Bjorn Andersson <Bjorn.Andersson@xxxxxxxxxxxxxx> wrote:

diff --git a/Documentation/devicetree/bindings/mfd/qcom-rpm-smd.txt b/Documentation/devicetree/bindings/mfd/qcom-rpm-smd.txt
new file mode 100644
index 0000000..a846101
--- /dev/null
+++ b/Documentation/devicetree/bindings/mfd/qcom-rpm-smd.txt
@@ -0,0 +1,122 @@
+Qualcomm Resource Power Manager (RPM) over SMD
+
+This driver is used to interface with the Resource Power Manager (RPM) found in
+various Qualcomm platforms. The RPM allows each component in the system to vote
+for state of the system resources, such as clocks, regulators and bus
+frequencies.
+
+- compatible:
+ Usage: required
+ Value type: <string>
+ Definition: must be one of:
+ "qcom,rpm-msm8974”

Why not “qcom,rpm-smd”. I’d like to get Jeff H’s input on how
what we do here for compat and distinguish the A-family RPM support vs
B-family/RPM-SMD support.


I don't see anything indicating changes in the actual communication, but as
this also encodes what resources are exposed we have to keep this specific.

I'm not sure what you mean with distinguish the A and B family, they are
completely different and there are no overlap in compatibles or implementation.

The overlap is in how children are communicating with the rpm, but this is an
implementation detail - and noted in that patch as a future improvement.


I forgot to add Jeff, but did send him a separate email asking for his input on
all this.


Yep. I saw the series. Still doing a deep dive.

The rpm-smd driver (and the A family equivalent) is outside of my area
of expertise, but I have some familiarity with it as it is a SMD client.
Internally we have a singular compat for all of B family, but I
haven't been able to figure out how that works to expose all of the
resources. I'll talk to my contact later in the week to see what the
differences are.


That's right, because you have these tables in devicetree in the caf version.
You have to have this information somewhere!

True, it must exist somewhere. However since its information tied directly to the hardware, it seems like its information that would fit right in DT.

I talked to my contact, and it seems like the table attributes vary more than I thought, target to target, so the single table design seems less plausible. Its my understanding you've had an offline discussion with him and some of our regulator guys to discuss the specifics of our needs. I'll let them take over as the experts.


Is the per target compat the way to do this though? The way its
currently done means we'll have atleast a dozen tables in
qcom-smd-rpm.c, and I can't imagine they will have anything more than
minor differences from the msm8x74_resource_table that currently exists
in patch 6 of the series. Why wouldn't one table that is a superset of
all supported targets work?


It would work as long as e.g. QCOM_RPM_PM8941_MVS1 always is vsa number 4.

But sure, it's a much better fit than the family a and this rpm would reject
invalid resources, so it might work. But this works without us knowing about
all possible platforms.


But if the case is that multiple platforms expose the same table we can always
tie the same table to multiple compatibles.

Regards,
Bjorn



--
Jeffrey Hugo
Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
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