phy: stm32: Fix constant-value overflow assertion

Rework the workaround as the lookup tables always fits into the bitfield,
and the default values are defined by the hardware and cannot be 0:

Guard against false positive with a WARN_ON check to make the compiler
happy: The offset range is pre-checked against the sorted imp_lookup_table
values and overflow should not happen and would be caught by a warning and
return in error.

Also guard against a true positive found during the max_vswing lookup, as a
max vswing value can be 802000 or 803000 microvolt depending on the current
impedance. Therefore set the default impedence index.

Fixes: 2de679e ("phy: stm32: work around constant-value overflow assertion")
Signed-off-by: Christian Bruel <christian.bruel@foss.st.com>
Link: https://lore.kernel.org/r/20250210103515.2598377-1-christian.bruel@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Christian Bruel

drivers/phy/st/phy-stm32-combophy.c

@@ -111,6 +111,7 @@ static const struct clk_impedance imp_lookup[] = {
 	{ 4204000, { 511000, 609000, 706000, 802000 } },
 	{ 3999000, { 571000, 648000, 726000, 803000 } }
 };
+#define DEFAULT_IMP_INDEX 3 /* Default impedance is 50 Ohm */
 
 static int stm32_impedance_tune(struct stm32_combophy *combophy)
 {
@@ -119,56 +120,53 @@ static int stm32_impedance_tune(struct stm32_combophy *combophy)
 	u8 imp_of, vswing_of;
 	u32 max_imp = imp_lookup[0].microohm;
 	u32 min_imp = imp_lookup[imp_size - 1].microohm;
-	u32 max_vswing = imp_lookup[imp_size - 1].vswing[vswing_size - 1];
+	u32 max_vswing;
 	u32 min_vswing = imp_lookup[0].vswing[0];
 	u32 val;
-	u32 regval;
 
 	if (!of_property_read_u32(combophy->dev->of_node, "st,output-micro-ohms", &val)) {
 		if (val < min_imp || val > max_imp) {
 			dev_err(combophy->dev, "Invalid value %u for output ohm\n", val);
 			return -EINVAL;
 		}
 
-		regval = 0;
-		for (imp_of = 0; imp_of < ARRAY_SIZE(imp_lookup); imp_of++) {
-			if (imp_lookup[imp_of].microohm <= val) {
-				regval = FIELD_PREP(STM32MP25_PCIEPRG_IMPCTRL_OHM, imp_of);
+		for (imp_of = 0; imp_of < ARRAY_SIZE(imp_lookup); imp_of++)
+			if (imp_lookup[imp_of].microohm <= val)
 				break;
-			}
-		}
+
+		if (WARN_ON(imp_of == ARRAY_SIZE(imp_lookup)))
+			return -EINVAL;
 
 		dev_dbg(combophy->dev, "Set %u micro-ohms output impedance\n",
 			imp_lookup[imp_of].microohm);
 
 		regmap_update_bits(combophy->regmap, SYSCFG_PCIEPRGCR,
 				   STM32MP25_PCIEPRG_IMPCTRL_OHM,
-				   regval);
-	} else {
-		regmap_read(combophy->regmap, SYSCFG_PCIEPRGCR, &val);
-		imp_of = FIELD_GET(STM32MP25_PCIEPRG_IMPCTRL_OHM, val);
-	}
+				   FIELD_PREP(STM32MP25_PCIEPRG_IMPCTRL_OHM, imp_of));
+	} else
+		imp_of = DEFAULT_IMP_INDEX;
 
 	if (!of_property_read_u32(combophy->dev->of_node, "st,output-vswing-microvolt", &val)) {
+		max_vswing = imp_lookup[imp_of].vswing[vswing_size - 1];
+
 		if (val < min_vswing || val > max_vswing) {
 			dev_err(combophy->dev, "Invalid value %u for output vswing\n", val);
 			return -EINVAL;
 		}
 
-		regval = 0;
-		for (vswing_of = 0; vswing_of < ARRAY_SIZE(imp_lookup[imp_of].vswing); vswing_of++) {
-			if (imp_lookup[imp_of].vswing[vswing_of] >= val) {
-				regval = FIELD_PREP(STM32MP25_PCIEPRG_IMPCTRL_VSWING, vswing_of);
+		for (vswing_of = 0; vswing_of < ARRAY_SIZE(imp_lookup[imp_of].vswing); vswing_of++)
+			if (imp_lookup[imp_of].vswing[vswing_of] >= val)
 				break;
-			}
-		}
+
+		if (WARN_ON(vswing_of == ARRAY_SIZE(imp_lookup[imp_of].vswing)))
+			return -EINVAL;
 
 		dev_dbg(combophy->dev, "Set %u microvolt swing\n",
 			 imp_lookup[imp_of].vswing[vswing_of]);
 
 		regmap_update_bits(combophy->regmap, SYSCFG_PCIEPRGCR,
 				   STM32MP25_PCIEPRG_IMPCTRL_VSWING,
-				   regval);
+				   FIELD_PREP(STM32MP25_PCIEPRG_IMPCTRL_VSWING, vswing_of));
 	}
 
 	return 0;