PM / devfreq: rk3399_dmc: Fix kernel oops when rockchip,pmu is absent

Booting a recent kernel on a rk3399-based system (nanopc-t4),
equipped with a recent u-boot and ATF results in an Oops due
to a NULL pointer dereference.

This turns out to be due to the rk3399-dmc driver looking for
an *undocumented* property (rockchip,pmu), and happily using
a NULL pointer when the property isn't there.

Instead, make most of what was brought in with 9173c5ce
("PM / devfreq: rk3399_dmc: Pass ODT and auto power down parameters
to TF-A.") conditioned on finding this property in the device-tree,
preventing the driver from exploding.

Cc: stable@vger.kernel.org
Fixes: 9173c5ce ("PM / devfreq: rk3399_dmc: Pass ODT and auto power down parameters to TF-A.")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/rk3399_dmc.c

@@ -95,18 +95,20 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
 
 	mutex_lock(&dmcfreq->lock);
 
+	if (dmcfreq->regmap_pmu) {
 		if (target_rate >= dmcfreq->odt_dis_freq)
 			odt_enable = true;
 
 		/*
-	 * This makes a SMC call to the TF-A to set the DDR PD (power-down)
-	 * timings and to enable or disable the ODT (on-die termination)
-	 * resistors.
+		 * This makes a SMC call to the TF-A to set the DDR PD
+		 * (power-down) timings and to enable or disable the
+		 * ODT (on-die termination) resistors.
 		 */
 		arm_smccc_smc(ROCKCHIP_SIP_DRAM_FREQ, dmcfreq->odt_pd_arg0,
 			      dmcfreq->odt_pd_arg1,
 			      ROCKCHIP_SIP_CONFIG_DRAM_SET_ODT_PD,
 			      odt_enable, 0, 0, 0, &res);
+	}
 
 	/*
 	 * If frequency scaling from low to high, adjust voltage first.
@@ -371,14 +373,15 @@ static int rk3399_dmcfreq_probe(struct platform_device *pdev)
 	}
 
 	node = of_parse_phandle(np, "rockchip,pmu", 0);
-	if (node) {
+	if (!node)
+		goto no_pmu;
+
 	data->regmap_pmu = syscon_node_to_regmap(node);
 	of_node_put(node);
 	if (IS_ERR(data->regmap_pmu)) {
 		ret = PTR_ERR(data->regmap_pmu);
 		goto err_edev;
 	}
-	}
 
 	regmap_read(data->regmap_pmu, RK3399_PMUGRF_OS_REG2, &val);
 	ddr_type = (val >> RK3399_PMUGRF_DDRTYPE_SHIFT) &
@@ -399,6 +402,7 @@ static int rk3399_dmcfreq_probe(struct platform_device *pdev)
 		goto err_edev;
 	};
 
+no_pmu:
 	arm_smccc_smc(ROCKCHIP_SIP_DRAM_FREQ, 0, 0,
 		      ROCKCHIP_SIP_CONFIG_DRAM_INIT,
 		      0, 0, 0, 0, &res);