ACPI: CPPC: Optimize cppc_get_perf()

Optimize cppc_get_perf() with three changes:

 1. Change the error kind to "no such device" when pcc_ss_id < 0, as
    other register value getting functions.

 2. Add a check to ensure the pointer 'perf' is no null.

 3. Add a check to verify if the register is supported to be read before
    using it. The logic is:

    (1) If the register is of the integer type, check whether the
        register is optional and its value is 0. If yes, the register
        is not supported.

    (2) If the register is of other types, a null one is not supported.

 4. Return the result of cpc_read() instead of 0.

Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20250411093855.982491-3-zhenglifeng1@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 34df03755699..a0774517642f 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1184,6 +1184,9 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
 	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
 	struct cpc_register_resource *reg;
 
+	if (perf == NULL)
+		return -EINVAL;
+
 	if (!cpc_desc) {
 		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
 		return -ENODEV;
@@ -1191,20 +1194,29 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
 
 	reg = &cpc_desc->cpc_regs[reg_idx];
 
+	if ((reg->type == ACPI_TYPE_INTEGER && IS_OPTIONAL_CPC_REG(reg_idx) &&
+	     !reg->cpc_entry.int_value) || (reg->type != ACPI_TYPE_INTEGER &&
+	     IS_NULL_REG(&reg->cpc_entry.reg))) {
+		pr_debug("CPC register is not supported\n");
+		return -EOPNOTSUPP;
+	}
+
 	if (CPC_IN_PCC(reg)) {
 		int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
 		struct cppc_pcc_data *pcc_ss_data = NULL;
-		int ret = 0;
+		int ret;
 
-		if (pcc_ss_id < 0)
-			return -EIO;
+		if (pcc_ss_id < 0) {
+			pr_debug("Invalid pcc_ss_id\n");
+			return -ENODEV;
+		}
 
 		pcc_ss_data = pcc_data[pcc_ss_id];
 
 		down_write(&pcc_ss_data->pcc_lock);
 
 		if (send_pcc_cmd(pcc_ss_id, CMD_READ) >= 0)
-			cpc_read(cpunum, reg, perf);
+			ret = cpc_read(cpunum, reg, perf);
 		else
 			ret = -EIO;
 
@@ -1213,9 +1225,7 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
 		return ret;
 	}
 
-	cpc_read(cpunum, reg, perf);
-
-	return 0;
+	return cpc_read(cpunum, reg, perf);
 }
 
 /**