ACPI: PMIC: Fix intel_pmic_regs_handler() read accesses

The handling of PMIC register reads through writing 0 to address 4
of the OpRegion is wrong. Instead of returning the read value
through the value64, which is a no-op for function == ACPI_WRITE calls,
store the value and then on a subsequent function == ACPI_READ with
address == 3 (the address for the value field of the OpRegion)
return the stored value.

This has been tested on a Xiaomi Mi Pad 2 and makes the ACPI battery dev
there mostly functional (unfortunately there are still other issues).

Here are the SET() / GET() functions of the PMIC ACPI device,
which use this OpRegion, which clearly show the new behavior to
be correct:

OperationRegion (REGS, 0x8F, Zero, 0x50)
Field (REGS, ByteAcc, NoLock, Preserve)
{
    CLNT,   8,
    SA,     8,
    OFF,    8,
    VAL,    8,
    RWM,    8
}

Method (GET, 3, Serialized)
{
    If ((AVBE == One))
    {
        CLNT = Arg0
        SA = Arg1
        OFF = Arg2
        RWM = Zero
        If ((AVBG == One))
        {
            GPRW = Zero
        }
    }

    Return (VAL) /* \_SB_.PCI0.I2C7.PMI5.VAL_ */
}

Method (SET, 4, Serialized)
{
    If ((AVBE == One))
    {
        CLNT = Arg0
        SA = Arg1
        OFF = Arg2
        VAL = Arg3
        RWM = One
        If ((AVBG == One))
        {
            GPRW = One
        }
    }
}

Fixes: 0afa877a ("ACPI / PMIC: intel: add REGS operation region support")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/pmic/intel_pmic.c

@@ -211,31 +211,36 @@ static acpi_status intel_pmic_regs_handler(u32 function,
 		void *handler_context, void *region_context)
 {
 	struct intel_pmic_opregion *opregion = region_context;
-	int result = 0;
+	int result = -EINVAL;
+
+	if (function == ACPI_WRITE) {
+		switch (address) {
+		case 0:
+			return AE_OK;
+		case 1:
+			opregion->ctx.addr |= (*value64 & 0xff) << 8;
+			return AE_OK;
+		case 2:
+			opregion->ctx.addr |= *value64 & 0xff;
+			return AE_OK;
+		case 3:
+			opregion->ctx.val = *value64 & 0xff;
+			return AE_OK;
+		case 4:
+			if (*value64) {
+				result = regmap_write(opregion->regmap, opregion->ctx.addr,
+						      opregion->ctx.val);
+			} else {
+				result = regmap_read(opregion->regmap, opregion->ctx.addr,
+						     &opregion->ctx.val);
+			}
+			opregion->ctx.addr = 0;
+		}
+	}
 
-	switch (address) {
-	case 0:
-		return AE_OK;
-	case 1:
-		opregion->ctx.addr |= (*value64 & 0xff) << 8;
-		return AE_OK;
-	case 2:
-		opregion->ctx.addr |= *value64 & 0xff;
+	if (function == ACPI_READ && address == 3) {
+		*value64 = opregion->ctx.val;
 		return AE_OK;
-	case 3:
-		opregion->ctx.val = *value64 & 0xff;
-		return AE_OK;
-	case 4:
-		if (*value64) {
-			result = regmap_write(opregion->regmap, opregion->ctx.addr,
-					      opregion->ctx.val);
-		} else {
-			result = regmap_read(opregion->regmap, opregion->ctx.addr,
-					     &opregion->ctx.val);
-			if (result == 0)
-				*value64 = opregion->ctx.val;
-		}
-		memset(&opregion->ctx, 0x00, sizeof(opregion->ctx));
 	}
 
 	if (result < 0) {