Re: [PATCH 1/4] dt-bindings: reset: Add PDC reset binding for SDM845 SoCs

From: Sibi Sankar
Date: Wed Aug 08 2018 - 11:44:15 EST

Hi Rob,
Thanks for the review

On 08/07/2018 11:46 PM, Rob Herring wrote:
On Tue, Jul 31, 2018 at 06:27:24PM +0530, Sibi S wrote:
Hi Philipp,
Thanks for the review!

On 07/31/2018 02:12 PM, Philipp Zabel wrote:
Hi Sibi,

On Fri, 2018-07-27 at 20:58 +0530, Sibi Sankar wrote:
Add SDM845 PDC (Power Domain Controller) reset controller binding

Signed-off-by: Sibi Sankar <sibis@xxxxxxxxxxxxxx>
.../bindings/reset/qcom,pdc-reset.txt | 52 +++++++++++++++++++
include/dt-bindings/reset/qcom,sdm845-pdc.h | 20 +++++++
2 files changed, 72 insertions(+)
create mode 100644 Documentation/devicetree/bindings/reset/qcom,pdc-reset.txt
create mode 100644 include/dt-bindings/reset/qcom,sdm845-pdc.h

diff --git a/Documentation/devicetree/bindings/reset/qcom,pdc-reset.txt b/Documentation/devicetree/bindings/reset/qcom,pdc-reset.txt
new file mode 100644
index 000000000000..85e159962e08
--- /dev/null
+++ b/Documentation/devicetree/bindings/reset/qcom,pdc-reset.txt
@@ -0,0 +1,52 @@
+PDC Reset Controller
+This binding describes a reset-controller found on PDC-Global(Power Domain
+Controller) block for Qualcomm Technologies Inc SDM845 SoCs.
+Required properties:
+- compatible:
+ Usage: required
+ Value type: <string>
+ Definition: must be:
+ "qcom,sdm845-pdc-global"
+- reg:
+ Usage: required
+ Value type: <prop-encoded-array>
+ Definition: must specify the base address and size of the register
+ space.
+- #reset-cells:
+ Usage: required
+ Value type: <uint>
+ Definition: must be 1; cell entry represents the reset index.
+pdc_reset: reset-controller@b2e0000 {

Is this really just a reset controller?

The name makes it sound like a driver binding to this should also
provide pm_genpd and the binding should probably call this a power-
controller: Documentation/devicetree/bindings/power/power_domain.txt.

The PDC-global reg space which is a part of PDC-wrapper reg space seems
to be only used for the reset lines.

Couple of other drivers use other parts of the PDC-wrapper reg space: (PDC-Interrupt controller) (GMU-PDC incorrectly tries
to occupy the entire pdc-wrapper reg space)

since it couldn't be logically mapped into pdc-interrupt driver, it had
to be included as a separate reset driver.

You can't have overlapping regions in DT (well, you can because we have
to work-around existing DTs that do, but you shouldn't).

A single node can be multiple providers such as interrupt controller and
reset controller. It's an OS problem to split that into multiple

There will be no overlaps. Jordan will be changing the dt binding of
gmu_pdc so that there is no overlap I guess. What I meant to say is that
pdc-global is a separate reg-space and currently has no other
functionality other than exposing the reset lines.

+ compatible = "qcom,sdm845-pdc-global";
+ reg = <0xb2e0000 0x20000>;

This looks like this is the register space of the complete PDC, not just
the reset register?

The entire register space was chosen because it is only used for its
reset lines (had a good look at the downstream kernel and had a conversation
with Lina) and to ensure break backward compatibility for
the for the dt entry if the reg-space was used for other purposes in
the future.

Why do you want to ensure breaking backwards compatibility?

Similar to the AOSS reset driver which had a unused clock part, this
driver also exposes a reg space of which only reset lines are used.


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