intelblocks/pcie: Correct mapping between LCAP port and coreboot index

coreboot uses port index which is 0 based for all PCIe root ports.
In case of PCIe remapping logic, coreboot reads LCAP register from PCIe
configuration space which contains port number (mostly 1 based). This
assumption might not be true for all the ports in coreboot.

TBT's LCAP registers are returning port index which are based on 2.
coreboot's PCIe remapping logic returns port index based on index 1.

This patch adds variable to pcie_rp_config to pass lcap_port_base to the
pcie remapping function, so coreboot can map any n-based LCAP encoding
to 0-based indexing scheme.

This patch updates correct lcap_port_base variable for all PCIe root
ports for all SOCs, so that function returns correct 0-based index from
LCAP port number.

BUG=b:210933428
BRANCH=None
TEST=Check if code compiles for all ADL boards

Change-Id: I7f9c3c8e753b982e2ede1a41bf87d6355b82da0f
Signed-off-by: MAULIK V VAGHELA <maulik.v.vaghela@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61936
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

2 files changed, 17 insertions, 6 deletions

diff --git a/src/soc/intel/common/block/include/intelblocks/pcie_rp.h b/src/soc/intel/common/block/include/intelblocks/pcie_rp.h
index b43987d13c..2f3b83ce4c 100644
--- a/src/soc/intel/common/block/include/intelblocks/pcie_rp.h
+++ b/src/soc/intel/common/block/include/intelblocks/pcie_rp.h
@@ -62,11 +62,17 @@ struct pcie_rp_config {
  * in case the root port numbers are not contiguous within the slot.
  * `count` is the number of functions within the group starting with the `start`
  * function number.
+ * `lcap_port_base` is the starting index of physical port as described in LCAP
+ * register in PCIe config space. coreboot always uses 0 based indexing while
+ * referring to the PCIe port but LCAP registers uses 1-based indexing in
+ * most of the cases. Remapping logic needs to correctly map LCAP port number
+ * (1-based or n-based) to coreboot indexing (0-based).
  */
 struct pcie_rp_group {
 	unsigned int slot;
 	unsigned int start;
 	unsigned int count;
+	unsigned int lcap_port_base;
 };
 
 static inline unsigned int rp_start_fn(const struct pcie_rp_group *group)
diff --git a/src/soc/intel/common/block/pcie/pcie_rp.c b/src/soc/intel/common/block/pcie/pcie_rp.c
index 221ee03a94..145159f6eb 100644
--- a/src/soc/intel/common/block/pcie/pcie_rp.c
+++ b/src/soc/intel/common/block/pcie/pcie_rp.c
@@ -31,20 +31,25 @@ static int pcie_rp_original_idx(
 	}
 
 	const uint32_t lcap = pci_s_read_config32(dev, clist + PCI_EXP_LNKCAP);
-	/* Read 1-based absolute port number. This reflects the numbering
-	   scheme that Intel uses in their documentation and what we use
-	   as index (0-based, though) in our mapping. */
+
+	/* Read n-based absolute port number from LCAP register.
+	   This reflects the numbering scheme that Intel uses in their
+	   documentation and what we use as index (0-based, though) in
+	   our mapping. */
 	const unsigned int port_num = (lcap & PCI_EXP_LNKCAP_PORT) >> 24;
 
-	/* `port_num` is 1-based, `offset` is 0-based. */
-	if (port_num <= offset || port_num > offset + group->count) {
+	/* Subtract lcap_port_base from port_num to get 0-based index */
+	const unsigned int port_idx = port_num - group->lcap_port_base;
+
+	/* Check if port_idx (0-based) is out of bounds */
+	if (port_idx < offset || port_idx >= offset + group->count) {
 		printk(BIOS_WARNING, "%s: Unexpected root-port number '%u'"
 				     " at PCI: 00:%02x.%x, ignoring.\n",
 		       __func__, port_num, group->slot, PCI_FUNC(PCI_DEV2DEVFN(dev)));
 		return -1;
 	}
 
-	return port_num - 1;
+	return port_idx;
 }
 
 /* Scan actual PCI config space to reconstruct current mapping */