[PATCH v2] phy: qcom-mipi-csi2: Add support for single power-domain SoCs

[Anusha Arun Nandi <anusha.nandi@oss.qualcomm.com>]

sa8775p, qcs8300 and sc7280 each list exactly one power-domain ("top")
on the CSI2 PHY node. For a device with a single power-domain phandle,
the generic platform-bus code (platform_probe() ->
dev_pm_domain_attach()) auto-attaches it via genpd_dev_pm_attach()
before the driver's own probe() runs. phy_qcom_mipi_csi2_probe() then
unconditionally calls devm_pm_domain_attach_list(), which fails with
-EEXIST because dev->pm_domain is already set, and the driver treats
that as fatal:

  1. qcom-mipi-csi2-phy ace6000.phy: error -EEXIST: Failed to attach
  power-domain list
  2. qcom-mipi-csi2-phy ace6000.phy: probe with driver qcom-mipi-csi2-phy
  failed with error -17

x1e80100 is unaffected: it lists three power-domains, so the generic
code does not auto-attach any of them (auto-attach only applies to
single-power-domain devices); the driver's explicit attach is the
only one that runs.

For the single power-domain case, call dev_pm_domain_attach() instead
of devm_pm_domain_attach_list(): it returns early when dev->pm_domain
is already set, so csi2phy->pd_list is left NULL rather than built up
by hand. The three call sites that walk pd_list for genpd
performance-state scaling now guard against a NULL pd_list, which is
harmless since scaling is unused (scaled = false) on every SoC that has
a single "top" domain.

Signed-off-by: Anusha Arun Nandi <anusha.nandi@oss.qualcomm.com>
---
 drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c b/drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c
index c0a4fa20eaf0..ac25e1e5f1c3 100644
--- a/drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c
+++ b/drivers/phy/qualcomm/phy-qcom-mipi-csi2-core.c
@@ -43,7 +43,7 @@ phy_qcom_mipi_csi2_set_clock_rates(struct mipi_csi2phy_device *csi2phy,
 	}
 
 	pstate = 0;
-	for (i = 0; i < csi2phy->pd_list->num_pds; i++) {
+	for (i = 0; csi2phy->pd_list && i < csi2phy->pd_list->num_pds; i++) {
 		unsigned int perf;
 
 		if (!csi2phy->soc_cfg->genpds[i].scaled)
@@ -174,7 +174,7 @@ static int phy_qcom_mipi_csi2_power_on(struct phy *phy)
 unset_rate:
 	dev_pm_opp_set_rate(csi2phy->dev, 0);
 
-	for (i = 0; i < csi2phy->pd_list->num_pds; i++) {
+	for (i = 0; csi2phy->pd_list && i < csi2phy->pd_list->num_pds; i++) {
 		if (!csi2phy->soc_cfg->genpds[i].scaled)
 			continue;
 
@@ -204,7 +204,7 @@ static int phy_qcom_mipi_csi2_power_off(struct phy *phy)
 
 	dev_pm_opp_set_rate(csi2phy->dev, 0);
 
-	for (i = 0; i < csi2phy->pd_list->num_pds; i++) {
+	for (i = 0; csi2phy->pd_list && i < csi2phy->pd_list->num_pds; i++) {
 		if (!csi2phy->soc_cfg->genpds[i].scaled)
 			continue;
 
@@ -233,6 +233,10 @@ static int phy_qcom_mipi_csi2_attach_pm_domains(struct mipi_csi2phy_device *csi2
 	const char **pd_names;
 	int i;
 
+	/* Single power-domain devices are already attached by the bus core. */
+	if (csi2phy->soc_cfg->num_genpds == 1)
+		return dev_pm_domain_attach(csi2phy->dev, 0);
+
 	pd_names = devm_kzalloc(csi2phy->dev,
 				sizeof(char *) * csi2phy->soc_cfg->num_genpds,
 				GFP_KERNEL);
@@ -369,11 +373,8 @@ static int phy_qcom_mipi_csi2_probe(struct platform_device *pdev)
 		return ret;
 
 	ret = phy_qcom_mipi_csi2_attach_pm_domains(csi2phy);
-	if (ret < 0 || csi2phy->pd_list == NULL) {
-		if (ret == 0)
-			ret = -ENODEV;
+	if (ret < 0)
 		return dev_err_probe(dev, ret, "Failed to attach power-domain list\n");
-	}
 
 	ret = devm_pm_runtime_enable(dev);
 	if (ret < 0)
-- 
2.34.1