PM / Domains: Enable genpd_dev_pm_attach_by_id|name() for single PM domain

If a call to dev_pm_domain_attach() succeeds to attach a device to its
single PM domain, the important point is to prevent subsequent
dev_pm_domain_attach_by_name|id() calls from failing. That is done by
checking the dev->pm_domain pointer and then returning -EEXIST, rather
than continuing to call genpd_dev_pm_attach_by_id|name().

For this reason, enable genpd_dev_pm_attach_by_id|name() to be used for
single PM domains too. This simplifies future users, so they only need
to use dev_pm_domain_attach_by_id|name() instead of having to combine
it with dev_pm_domain_attach().
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NNiklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/domain.c

@@ -2439,10 +2439,10 @@ struct device *genpd_dev_pm_attach_by_id(struct device *dev,
 	if (!dev->of_node)
 		return NULL;
 
-	/* Deal only with devices using multiple PM domains. */
+	/* Verify that the index is within a valid range. */
 	num_domains = of_count_phandle_with_args(dev->of_node, "power-domains",
 						 "#power-domain-cells");
-	if (num_domains < 2 || index >= num_domains)
+	if (index >= num_domains)
 		return NULL;
 
 	/* Allocate and register device on the genpd bus. */