soc/amd/common/blk/pcie: Program LTR max latencies

PCIe bridges need to provide the LTR (latency tolerance reporting)
maximum snoop/non-snoop values so that they are inherited by downstream
PCIe devices which support and enable LTR. Without this, downstream
devices cannot have LTR enabled, which is a requirement for supporting
PCIe L1 substates. Enabling L1ss without LTR has unpredictable behavior,
including some devices refusing to enter L1 low power modes at all.

Program the max snoop/non-snoop latency values for all PCIe bridges
using the same value used by AGESA/FSP, 1.049ms.

BUG=b:265890321
TEST=build/boot google/skyrim (multiple variants, NVMe drives), ensure
LTR is enabled, latency values are correctly set, and that device
power draw at idle is in the expected range (<25 mW).

Change-Id: Icf188e69cf5676be870873c56d175423d16704b4
Signed-off-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74288
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/soc/amd/common/block/pci/pcie_gpp.c b/src/soc/amd/common/block/pci/pcie_gpp.c
index 0ce3268501..0f983d04be 100644
--- a/src/soc/amd/common/block/pci/pcie_gpp.c
+++ b/src/soc/amd/common/block/pci/pcie_gpp.c
@@ -47,6 +47,20 @@ static void acpi_device_write_gpp_pci_dev(const struct device *dev)
 	acpigen_pop_len(); /* Scope */
 }
 
+/* Latency tolerance reporting, max snoop/non-snoop latency value 1.049ms */
+#define PCIE_LTR_MAX_LATENCY_1049US 0x1001
+
+static void pcie_get_ltr_max_latencies(u16 *max_snoop, u16 *max_nosnoop)
+{
+	*max_snoop = PCIE_LTR_MAX_LATENCY_1049US;
+	*max_nosnoop = PCIE_LTR_MAX_LATENCY_1049US;
+}
+
+static struct pci_operations pcie_ops = {
+	.get_ltr_max_latencies	= pcie_get_ltr_max_latencies,
+	.set_subsystem		= pci_dev_set_subsystem,
+};
+
 struct device_operations amd_internal_pcie_gpp_ops = {
 	.read_resources		= pci_bus_read_resources,
 	.set_resources		= pci_dev_set_resources,
@@ -65,4 +79,5 @@ struct device_operations amd_external_pcie_gpp_ops = {
 	.reset_bus		= pci_bus_reset,
 	.acpi_name		= pcie_gpp_acpi_name,
 	.acpi_fill_ssdt		= acpi_device_write_gpp_pci_dev,
+	.ops_pci		= &pcie_ops,
 };