[RFC][PATCH 3/6] ACPI: processor: Clean up acpi_processor_evaluate_cst()

Rafael J. Wysocki
2019-12-06T09:49:38Z

Clean up acpi_processor_evaluate_cst() in multiple ways:

* Rename current_count to last_index which matches the purpose of
the variable better.

* Consistently use acpi_handle_*() for printing messages and make
the messages cleaner.

* Drop redundant parens and braces.

* Rewrite and clarify comments.

* Rearrange checks and drop the redundant ones.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/acpi/processor_idle.c | 114 +++++++++++++++++++-----------------------
1 file changed, 52 insertions(+), 62 deletions(-)

Index: linux-pm/drivers/acpi/processor_idle.c
===================================================================
--- linux-pm.orig/drivers/acpi/processor_idle.c
+++ linux-pm/drivers/acpi/processor_idle.c
@@ -304,29 +304,29 @@ static int acpi_processor_evaluate_cst(a
union acpi_object *cst;
acpi_status status;
u64 count;
- int current_count = 0;
+ int last_index = 0;
int i, ret = 0;

status = acpi_evaluate_object(handle, "_CST", NULL, &buffer);
if (ACPI_FAILURE(status)) {
- ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No _CST, giving up\n"));
+ acpi_handle_debug(handle, "No _CST\n");
return -ENODEV;
}

cst = buffer.pointer;

- /* There must be at least 2 elements */
- if (!cst || (cst->type != ACPI_TYPE_PACKAGE) || cst->package.count < 2) {
- pr_err("not enough elements in _CST\n");
+ /* There must be at least 2 elements. */
+ if (!cst || cst->type != ACPI_TYPE_PACKAGE || cst->package.count < 2) {
+ acpi_handle_warn(handle, "Invalid _CST output\n");
ret = -EFAULT;
goto end;
}

count = cst->package.elements[0].integer.value;

- /* Validate number of power states. */
+ /* Validate the number of C-states. */
if (count < 1 || count != cst->package.count - 1) {
- pr_err("count given by _CST is not valid\n");
+ acpi_handle_warn(handle, "Inconsistent _CST data\n");
ret = -EFAULT;
goto end;
}
@@ -337,111 +337,101 @@ static int acpi_processor_evaluate_cst(a
struct acpi_power_register *reg;
struct acpi_processor_cx cx;

+ /*
+ * If there is not enough space for all C-states, skip the
+ * excess ones and log a warning.
+ */
+ if (last_index >= ACPI_PROCESSOR_MAX_POWER - 1) {
+ acpi_handle_warn(handle,
+ "No room for more idle states (limit: %d)\n",
+ ACPI_PROCESSOR_MAX_POWER - 1);
+ break;
+ }
+
memset(&cx, 0, sizeof(cx));

- element = &(cst->package.elements[i]);
+ element = &cst->package.elements[i];
if (element->type != ACPI_TYPE_PACKAGE)
continue;

if (element->package.count != 4)
continue;

- obj = &(element->package.elements[0]);
+ obj = &element->package.elements[0];

if (obj->type != ACPI_TYPE_BUFFER)
continue;

reg = (struct acpi_power_register *)obj->buffer.pointer;

- if (reg->space_id != ACPI_ADR_SPACE_SYSTEM_IO &&
- (reg->space_id != ACPI_ADR_SPACE_FIXED_HARDWARE))
- continue;
-
- /* There should be an easy way to extract an integer... */
- obj = &(element->package.elements[1]);
+ obj = &element->package.elements[1];
if (obj->type != ACPI_TYPE_INTEGER)
continue;

cx.type = obj->integer.value;
/*
- * Some buggy BIOSes won't list C1 in _CST -
- * Let acpi_processor_get_power_info_default() handle them later
+ * There are known cases in which the _CST output does not
+ * contain C1, so if the type of the first state found is not
+ * C1, leave an empty slot for C1 to be filled in later.
*/
if (i == 1 && cx.type != ACPI_STATE_C1)
- current_count++;
+ last_index = 1;

cx.address = reg->address;
- cx.index = current_count + 1;
+ cx.index = last_index + 1;

- cx.entry_method = ACPI_CSTATE_SYSTEMIO;
if (reg->space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) {
- if (acpi_processor_ffh_cstate_probe
- (cpu, &cx, reg) == 0) {
- cx.entry_method = ACPI_CSTATE_FFH;
+ if (!acpi_processor_ffh_cstate_probe(cpu, &cx, reg)) {
+ /*
+ * In the majority of cases _CST describes C1 as
+ * a FIXED_HARDWARE C-state, but if the command
+ * line forbids using MWAIT, use CSTATE_HALT for
+ * C1 regardless.
+ */
+ if (cx.type == ACPI_STATE_C1 &&
+ boot_option_idle_override == IDLE_NOMWAIT) {
+ cx.entry_method = ACPI_CSTATE_HALT;
+ snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");
+ } else {
+ cx.entry_method = ACPI_CSTATE_FFH;
+ }
} else if (cx.type == ACPI_STATE_C1) {
/*
- * C1 is a special case where FIXED_HARDWARE
- * can be handled in non-MWAIT way as well.
- * In that case, save this _CST entry info.
- * Otherwise, ignore this info and continue.
+ * In the special case of C1, FIXED_HARDWARE can
+ * be handled by executing the HLT instruction.
*/
cx.entry_method = ACPI_CSTATE_HALT;
snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");
} else {
continue;
}
- if (cx.type == ACPI_STATE_C1 &&
- (boot_option_idle_override == IDLE_NOMWAIT)) {
- /*
- * In most cases the C1 space_id obtained from
- * _CST object is FIXED_HARDWARE access mode.
- * But when the option of idle=halt is added,
- * the entry_method type should be changed from
- * CSTATE_FFH to CSTATE_HALT.
- * When the option of idle=nomwait is added,
- * the C1 entry_method type should be
- * CSTATE_HALT.
- */
- cx.entry_method = ACPI_CSTATE_HALT;
- snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI HLT");
- }
- } else {
+ } else if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
+ cx.entry_method = ACPI_CSTATE_SYSTEMIO;
snprintf(cx.desc, ACPI_CX_DESC_LEN, "ACPI IOPORT 0x%x",
cx.address);
+ } else {
+ continue;
}

- if (cx.type == ACPI_STATE_C1) {
+ if (cx.type == ACPI_STATE_C1)
cx.valid = 1;
- }

- obj = &(element->package.elements[2]);
+ obj = &element->package.elements[2];
if (obj->type != ACPI_TYPE_INTEGER)
continue;

cx.latency = obj->integer.value;

- obj = &(element->package.elements[3]);
+ obj = &element->package.elements[3];
if (obj->type != ACPI_TYPE_INTEGER)
continue;

- current_count++;
- memcpy(&info->states[current_count], &cx, sizeof(cx));
-
- /*
- * We support total ACPI_PROCESSOR_MAX_POWER - 1
- * (From 1 through ACPI_PROCESSOR_MAX_POWER - 1)
- */
- if (current_count >= (ACPI_PROCESSOR_MAX_POWER - 1)) {
- pr_warn("Limiting number of power states to max (%d)\n",
- ACPI_PROCESSOR_MAX_POWER);
- pr_warn("Please increase ACPI_PROCESSOR_MAX_POWER if needed.\n");
- break;
- }
+ memcpy(&info->states[++last_index], &cx, sizeof(cx));
}

- acpi_handle_info(handle, "Found %d idle states\n", current_count);
+ acpi_handle_info(handle, "Found %d idle states\n", last_index);

- info->count = current_count;
+ info->count = last_index;

end:
kfree(buffer.pointer);