[PATCH V2 4/9] PCI/TPH: Implement a command line option to force No ST Mode

Wei Huang
2024-05-31T21:39:56Z

When "No ST mode" is enabled, end-point devices can generate TPH headers
but with all steering tags treated as zero. A steering tag of zero is
interpreted as "using the default policy" by the root complex. This is
essential to quantify the benefit of steering tags for some given
workloads.

Co-developed-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Eric Van Tassell <Eric.VanTassell@amd.com>
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
---
.../admin-guide/kernel-parameters.txt | 1 +
drivers/pci/pci-driver.c | 7 ++++++-
drivers/pci/pci.c | 12 +++++++++++
drivers/pci/pcie/tph.c | 21 +++++++++++++++++++
include/linux/pci-tph.h | 3 +++
include/linux/pci.h | 1 +
6 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fedcc69e35c1..e97a4a239563 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4624,6 +4624,7 @@
norid [S390] ignore the RID field and force use of
one PCI domain per PCI function
notph [PCIE] Do not use PCIe TPH
+ nostmode [PCIE] Force TPH to use No ST Mode

pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power
Management.
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 9722d070c0ca..aa98843d9884 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -324,8 +324,13 @@ static long local_pci_probe(void *_ddi)
pci_dev->driver = pci_drv;
rc = pci_drv->probe(pci_dev, ddi->id);
if (!rc) {
- if (pci_tph_disabled())
+ if (pci_tph_disabled()) {
pcie_tph_disable(pci_dev);
+ return rc;
+ }
+
+ if (pci_tph_nostmode())
+ tph_set_dev_nostmode(pci_dev);

return rc;
}
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 31c443504ce9..f3558a551bf2 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -160,6 +160,9 @@ static bool pcie_ats_disabled;
/* If set, the PCIe TPH capability will not be used. */
static bool pcie_tph_disabled;

+/* If TPH is enabled, "No ST Mode" will be enforced. */
+static bool pcie_tph_nostmode;
+
/* If set, the PCI config space of each device is printed during boot. */
bool pci_early_dump;

@@ -175,6 +178,12 @@ bool pci_tph_disabled(void)
}
EXPORT_SYMBOL_GPL(pci_tph_disabled);

+bool pci_tph_nostmode(void)
+{
+ return pcie_tph_nostmode;
+}
+EXPORT_SYMBOL_GPL(pci_tph_nostmode);
+
/* Disable bridge_d3 for all PCIe ports */
static bool pci_bridge_d3_disable;
/* Force bridge_d3 for all PCIe ports */
@@ -6818,6 +6827,9 @@ static int __init pci_setup(char *str)
} else if (!strcmp(str, "notph")) {
pr_info("PCIe: TPH is disabled\n");
pcie_tph_disabled = true;
+ } else if (!strcmp(str, "nostmode")) {
+ pr_info("PCIe: TPH No ST Mode is enabled\n");
+ pcie_tph_nostmode = true;
} else if (!strncmp(str, "cbiosize=", 9)) {
pci_cardbus_io_size = memparse(str + 9, &str);
} else if (!strncmp(str, "cbmemsize=", 10)) {
diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
index 5dc533b89a33..d5f7309fdf52 100644
--- a/drivers/pci/pcie/tph.c
+++ b/drivers/pci/pcie/tph.c
@@ -43,6 +43,27 @@ static int tph_set_reg_field_u32(struct pci_dev *dev, u8 offset, u32 mask,
return ret;
}

+int tph_set_dev_nostmode(struct pci_dev *dev)
+{
+ int ret;
+
+ /* set ST Mode Select to "No ST Mode" */
+ ret = tph_set_reg_field_u32(dev, PCI_TPH_CTRL,
+ PCI_TPH_CTRL_MODE_SEL_MASK,
+ PCI_TPH_CTRL_MODE_SEL_SHIFT,
+ PCI_TPH_NO_ST_MODE);
+ if (ret)
+ return ret;
+
+ /* set "TPH Requester Enable" to "TPH only" */
+ ret = tph_set_reg_field_u32(dev, PCI_TPH_CTRL,
+ PCI_TPH_CTRL_REQ_EN_MASK,
+ PCI_TPH_CTRL_REQ_EN_SHIFT,
+ PCI_TPH_REQ_TPH_ONLY);
+
+ return ret;
+}
+
int pcie_tph_disable(struct pci_dev *dev)
{
return tph_set_reg_field_u32(dev, PCI_TPH_CTRL,
diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
index e187d7e89e8c..95269afc8b7d 100644
--- a/include/linux/pci-tph.h
+++ b/include/linux/pci-tph.h
@@ -11,9 +11,12 @@

#ifdef CONFIG_PCIE_TPH
int pcie_tph_disable(struct pci_dev *dev);
+int tph_set_dev_nostmode(struct pci_dev *dev);
#else
static inline int pcie_tph_disable(struct pci_dev *dev)
{ return -EOPNOTSUPP; }
+static inline int tph_set_dev_nostmode(struct pci_dev *dev)
+{ return -EOPNOTSUPP; }
#endif

#endif /* LINUX_PCI_TPH_H */
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d88ebe87815a..5f520624d133 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1842,6 +1842,7 @@ static inline bool pci_aer_available(void) { return false; }

bool pci_ats_disabled(void);
bool pci_tph_disabled(void);
+bool pci_tph_nostmode(void);

#ifdef CONFIG_PCIE_PTM
int pci_enable_ptm(struct pci_dev *dev, u8 *granularity);
--
2.44.0