soc: qcom: rpmpd: Add parent PD support

In some cases (like with the GPU core clock on GMU-less SoCs) it's
required that we scale more than one voltage domain. This can be achieved
by linking them in a parent-child relationship. Add support for specifying
a parent PD, similarly to what has been done in the RPMhPD driver.
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230313-topic-rpmpd-v3-8-06a4f448ff90@linaro.org

drivers/soc/qcom/rpmpd.c

@@ -48,6 +48,7 @@ struct rpmpd_req {
 
 struct rpmpd {
 	struct generic_pm_domain pd;
+	struct generic_pm_domain *parent;
 	struct rpmpd *peer;
 	const bool active_only;
 	unsigned int corner;
@@ -969,6 +970,15 @@ static int rpmpd_probe(struct platform_device *pdev)
 		data->domains[i] = &rpmpds[i]->pd;
 	}
 
+	/* Add subdomains */
+	for (i = 0; i < num; i++) {
+		if (!rpmpds[i])
+			continue;
+
+		if (rpmpds[i]->parent)
+			pm_genpd_add_subdomain(rpmpds[i]->parent, &rpmpds[i]->pd);
+	}
+
 	return of_genpd_add_provider_onecell(pdev->dev.of_node, data);
 }