Re: [RFC PATCH] PCI/APCI: Move acpi_pci_osc_support() check to negotiation phase

From: Kuppuswamy, Sathyanarayanan
Date: Wed Apr 28 2021 - 13:21:21 EST




On 4/28/21 1:18 AM, Joerg Roedel wrote:
From: Joerg Roedel <jroedel@xxxxxxx>

The acpi_pci_osc_support() does an _OSC query with _OSC supported set
to what the OS supports but a zero _OSC control value. This is
problematic on some platforms where the firmware allows to configure
whether DPC is under OS or Firmware control.

Do we run acpi_pci_osc_support() only to check whether _OSC is
supported ? Or does it serve any other purpose.



When DPC is configured to be under OS control these platforms will
issue a warning in the firmware log that the OS does not support DPC.

Also, is there any other benefit from this patch other than fixing
a warning message in firmware?


Avoid an _OSC query with _OSC control set to zero by moving the
supported check into the acpi_pci_osc_control_set() path. This is
still early enough to fail as nothing before that depends on the
results of acpi_pci_osc_support().

As a result the acpi_pci_osc_support() function can be removed and
acpi_pci_query_osc() be simplified because it no longer called with a
NULL pointer for *control.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
drivers/acpi/pci_root.c | 50 ++++++++++++++++-------------------------
1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index dcd593766a64..530ecf4970b1 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -199,16 +199,11 @@ static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
support &= OSC_PCI_SUPPORT_MASKS;
support |= root->osc_support_set;
+ *control &= OSC_PCI_CONTROL_MASKS;
capbuf[OSC_QUERY_DWORD] = OSC_QUERY_ENABLE;
capbuf[OSC_SUPPORT_DWORD] = support;
- if (control) {
- *control &= OSC_PCI_CONTROL_MASKS;
- capbuf[OSC_CONTROL_DWORD] = *control | root->osc_control_set;
- } else {
- /* Run _OSC query only with existing controls. */
- capbuf[OSC_CONTROL_DWORD] = root->osc_control_set;
- }
+ capbuf[OSC_CONTROL_DWORD] = *control | root->osc_control_set;
status = acpi_pci_run_osc(root->device->handle, capbuf, &result);
if (ACPI_SUCCESS(status)) {
@@ -219,11 +214,6 @@ static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
return status;
}
-static acpi_status acpi_pci_osc_support(struct acpi_pci_root *root, u32 flags)
-{
- return acpi_pci_query_osc(root, flags, NULL);
-}
-
struct acpi_pci_root *acpi_pci_find_root(acpi_handle handle)
{
struct acpi_pci_root *root;
@@ -346,7 +336,8 @@ EXPORT_SYMBOL_GPL(acpi_get_pci_dev);
* _OSC bits the BIOS has granted control of, but its contents are meaningless
* on failure.
**/
-static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 req)
+static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32
+ *mask, u32 req, u32 support)
{
struct acpi_pci_root *root;
acpi_status status;
@@ -370,7 +361,7 @@ static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 r
/* Need to check the available controls bits before requesting them. */
while (*mask) {
- status = acpi_pci_query_osc(root, root->osc_support_set, mask);
+ status = acpi_pci_query_osc(root, support, mask);
if (ACPI_FAILURE(status))
return status;
if (ctrl == *mask)
@@ -433,18 +424,6 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
support |= OSC_PCI_EDR_SUPPORT;
decode_osc_support(root, "OS supports", support);
- status = acpi_pci_osc_support(root, support);
- if (ACPI_FAILURE(status)) {
- *no_aspm = 1;
-
- /* _OSC is optional for PCI host bridges */
- if ((status == AE_NOT_FOUND) && !is_pcie)
- return;
-
- dev_info(&device->dev, "_OSC: platform retains control of PCIe features (%s)\n",
- acpi_format_exception(status));
- return;
- }
if (pcie_ports_disabled) {
dev_info(&device->dev, "PCIe port services disabled; not requesting _OSC control\n");
@@ -483,7 +462,8 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
requested = control;
status = acpi_pci_osc_control_set(handle, &control,
- OSC_PCI_EXPRESS_CAPABILITY_CONTROL);
+ OSC_PCI_EXPRESS_CAPABILITY_CONTROL,
+ support);
if (ACPI_SUCCESS(status)) {
decode_osc_control(root, "OS now controls", control);
if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM) {
@@ -496,10 +476,8 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
*no_aspm = 1;
}
} else {
- decode_osc_control(root, "OS requested", requested);
- decode_osc_control(root, "platform willing to grant", control);
- dev_info(&device->dev, "_OSC: platform retains control of PCIe features (%s)\n",
- acpi_format_exception(status));
+ /* Platform wants to control PCIe features */
+ root->osc_support_set = 0;
/*
* We want to disable ASPM here, but aspm_disabled
@@ -509,6 +487,16 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
* root scan.
*/
*no_aspm = 1;
+
+ /* _OSC is optional for PCI host bridges */
+ if ((status == AE_NOT_FOUND) && !is_pcie)
+ return;
+
+ decode_osc_control(root, "OS requested", requested);
+ decode_osc_control(root, "platform willing to grant", control);
+ dev_info(&device->dev, "_OSC: platform retains control of PCIe features (%s)\n",
+ acpi_format_exception(status));
+
}
}


--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer