Re: [PATCH v6 2/9] PCI/ACPI: Add _OSC based negotiation support for DPC

From: Kuppuswamy Sathyanarayanan
Date: Thu Aug 15 2019 - 19:47:31 EST


On 8/15/19 3:17 PM, Bjorn Helgaas wrote:
On Fri, Jul 26, 2019 at 02:43:12PM -0700, sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

As per PCI firmware specification r3.2 Downstream Port Containment
Related Enhancements ECN, sec 4.5.1, table 4-6, OS can use bit 7 of _OSC
Control Field to negotiate control over Downstream Port Containment
(DPC) configuration of PCIe port.

After _OSC negotiation, firmware will Set this bit to grant OS control
over PCIe DPC configuration and Clear it if this feature was requested
and denied, or was not requested.

Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---
drivers/acpi/pci_root.c | 6 ++++++
drivers/pci/pcie/portdrv_core.c | 3 ++-
drivers/pci/probe.c | 1 +
include/linux/acpi.h | 3 ++-
include/linux/pci.h | 2 +-
5 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 314a187ed572..73b08f40b0da 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -142,6 +142,7 @@ static struct pci_osc_bit_struct pci_osc_control_bit[] = {
{ OSC_PCI_EXPRESS_AER_CONTROL, "AER" },
{ OSC_PCI_EXPRESS_CAPABILITY_CONTROL, "PCIeCapability" },
{ OSC_PCI_EXPRESS_LTR_CONTROL, "LTR" },
+ { OSC_PCI_EXPRESS_DPC_CONTROL, "DPC" },
};
static void decode_osc_bits(struct acpi_pci_root *root, char *msg, u32 word,
@@ -488,6 +489,9 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
control |= OSC_PCI_EXPRESS_AER_CONTROL;
}
+ if (IS_ENABLED(CONFIG_PCIE_DPC))
+ control |= OSC_PCI_EXPRESS_DPC_CONTROL;
Sec 4.5.2.4 says:

If the OS sets bit 7 of the Control field, it must set bit 7 of the
Support field, indicating support for the Error Disconnect Recover
event.

I think the correct dependency should be , if OS indicates support for EDR then it must
set bit 7 of the Control field to indicate support for DPC. As per DPC control bit definition, setting
this bit indicates requesting control of DPC for OS (not EDR).

I will ask the spec author for clarification. But for now I will go with spec requirement, I will merge this
patch with "Expose EDR support via _OSC to BIOS" patch and push it to the end of the patch set.


I see that you do set bit 7 (OSC_PCI_EDR_SUPPORT) in the Support field
in a later patch, but I don't think we should have this intermediate
state where we set OSC_PCI_EXPRESS_DPC_CONTROL in Control but not
OSC_PCI_EDR_SUPPORT in Support.

requested = control;
status = acpi_pci_osc_control_set(handle, &control,
OSC_PCI_EXPRESS_CAPABILITY_CONTROL);
@@ -917,6 +921,8 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
host_bridge->native_pme = 0;
if (!(root->osc_control_set & OSC_PCI_EXPRESS_LTR_CONTROL))
host_bridge->native_ltr = 0;
+ if (!(root->osc_control_set & OSC_PCI_EXPRESS_DPC_CONTROL))
+ host_bridge->native_dpc = 0;
/*
* Evaluate the "PCI Boot Configuration" _DSM Function. If it
diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index 308c3e0c4a34..58c40fe7856f 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -252,7 +252,8 @@ static int get_port_device_capability(struct pci_dev *dev)
}
if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) &&
- pci_aer_available() && services & PCIE_PORT_SERVICE_AER)
+ pci_aer_available() && services & PCIE_PORT_SERVICE_AER &&
+ (pcie_ports_native || host->native_dpc))
services |= PCIE_PORT_SERVICE_DPC;
if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index a3c7338fad86..cf8acdd62089 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -601,6 +601,7 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
bridge->native_shpc_hotplug = 1;
bridge->native_pme = 1;
bridge->native_ltr = 1;
+ bridge->native_dpc = 1;
}
struct pci_host_bridge *pci_alloc_host_bridge(size_t priv)
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 9426b9aaed86..8959ed322e15 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -525,7 +525,8 @@ extern bool osc_pc_lpi_support_confirmed;
#define OSC_PCI_EXPRESS_AER_CONTROL 0x00000008
#define OSC_PCI_EXPRESS_CAPABILITY_CONTROL 0x00000010
#define OSC_PCI_EXPRESS_LTR_CONTROL 0x00000020
-#define OSC_PCI_CONTROL_MASKS 0x0000003f
+#define OSC_PCI_EXPRESS_DPC_CONTROL 0x00000080
+#define OSC_PCI_CONTROL_MASKS 0x000000ff
You added 0x80, but 0x3f | 0x80 == 0xbf, not 0xff, so I expected
OSC_PCI_CONTROL_MASKS would change to 0xbf. Why the difference?
Good catch. Even though spec has support for bit[6], it should be
masked till OS supports it. I will fix it in next version.

#define ACPI_GSB_ACCESS_ATTRIB_QUICK 0x00000002
#define ACPI_GSB_ACCESS_ATTRIB_SEND_RCV 0x00000004
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 9e700d9f9f28..9145136ca728 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -510,7 +510,7 @@ struct pci_host_bridge {
unsigned int native_pme:1; /* OS may use PCIe PME */
unsigned int native_ltr:1; /* OS may use PCIe LTR */
unsigned int preserve_config:1; /* Preserve FW resource setup */
-
+ unsigned int native_dpc:1; /* OS may use PCIe DPC */
Please put this next to the other "native_*" bits and preserve the
blank line.
ok.

/* Resource alignment requirements */
resource_size_t (*align_resource)(struct pci_dev *dev,
const struct resource *res,
--
2.21.0

--
Sathyanarayanan Kuppuswamy
Linux kernel developer