sb/intel/lynxpoint: Handle H81 only having 6 PCIe root ports

The H81 chipset is the only non-LP Lynx Point chipset with 6 PCIe root
ports, all others have 8 [1]. The existing PCIe code assumed that all
non-LP chipsets had 8 root ports, which meant that port 6 would not be
considered the last root port on H81, so `root_port_commit_config()`
would not run. Ultimately, while PCIe still worked on H81, all the root
ports would remain enabled, even if disabled in the devicetree.

Also, remove `PCI_DEVICE_ID_INTEL_LYNXPOINT_MOB_DESK_{MIN,MAX}`, as they
are unused, and the MAX constant is incorrect.

Interestingly, this fixes an issue where GRUB is unable to halt the
system.

Tested on an ASRock H81M-HDS. The root ports disabled in the devicetree
do indeed end up disabled.

[1] Intel® 8 Series/C220 Series Chipset Family Platform Controller Hub
    (PCH) Datasheet, revision 003, document number 328904.

Change-Id: If3ce217e8a4f4ea4e111e4525b03dbbfc63f92b0
Signed-off-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-on: https://review.coreboot.org/c/30077
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

3 files changed, 19 insertions, 9 deletions

diff --git a/src/southbridge/intel/lynxpoint/pch.c b/src/southbridge/intel/lynxpoint/pch.c
index 6596aa2f5d..1fb6d7ad54 100644
--- a/src/southbridge/intel/lynxpoint/pch.c
+++ b/src/southbridge/intel/lynxpoint/pch.c
@@ -45,6 +45,16 @@ int pch_silicon_revision(void)
 	return pch_revision_id;
 }
 
+int pch_silicon_id(void)
+{
+	static int pch_id = -1;
+
+	if (pch_id < 0)
+		pch_id = pci_read_config16(pch_get_lpc_device(), PCI_DEVICE_ID);
+
+	return pch_id;
+}
+
 int pch_silicon_type(void)
 {
 	static int pch_type = -1;
diff --git a/src/southbridge/intel/lynxpoint/pch.h b/src/southbridge/intel/lynxpoint/pch.h
index a28d703130..ee041d9dd2 100644
--- a/src/southbridge/intel/lynxpoint/pch.h
+++ b/src/southbridge/intel/lynxpoint/pch.h
@@ -141,6 +141,7 @@ struct rcba_config_instruction
 #if !defined(__ASSEMBLER__)
 void pch_config_rcba(const struct rcba_config_instruction *rcba_config);
 int pch_silicon_revision(void);
+int pch_silicon_id(void);
 int pch_silicon_type(void);
 int pch_is_lp(void);
 u16 get_pmbase(void);
diff --git a/src/southbridge/intel/lynxpoint/pcie.c b/src/southbridge/intel/lynxpoint/pcie.c
index 70bfe18242..750b53395c 100644
--- a/src/southbridge/intel/lynxpoint/pcie.c
+++ b/src/southbridge/intel/lynxpoint/pcie.c
@@ -23,10 +23,7 @@
 #include "pch.h"
 #include <southbridge/intel/common/gpio.h>
 
-/* LynxPoint-LP has 6 root ports while non-LP has 8. */
 #define MAX_NUM_ROOT_PORTS 8
-#define H_NUM_ROOT_PORTS MAX_NUM_ROOT_PORTS
-#define LP_NUM_ROOT_PORTS (MAX_NUM_ROOT_PORTS - 2)
 
 struct root_port_config {
 	/* RPFN is a write-once register so keep a copy until it is written */
@@ -49,10 +46,10 @@ static struct root_port_config rpc;
 
 static inline int max_root_ports(void)
 {
-	if (pch_is_lp())
-		return LP_NUM_ROOT_PORTS;
-	else
-		return H_NUM_ROOT_PORTS;
+	if (pch_is_lp() || pch_silicon_id() == PCI_DEVICE_ID_INTEL_LPT_H81)
+		return 6;
+
+	return 8;
 }
 
 static inline int root_port_is_first(struct device *dev)
@@ -208,8 +205,10 @@ static void pcie_enable_clock_gating(void)
 					pci_update_config8(dev, 0xe1, 0x7f, 0x80);
 				}
 				if (rp == 5 && !rpc.ports[5]->enabled &&
-				    !rpc.ports[6]->enabled &&
-				    !rpc.ports[7]->enabled) {
+				    (rpc.ports[6] == NULL ||
+				     !rpc.ports[6]->enabled) &&
+				    (rpc.ports[7] == NULL ||
+				     !rpc.ports[7]->enabled)) {
 					pci_update_config8(dev, 0xe2, ~1, 1);
 					pci_update_config8(dev, 0xe1, 0x7f, 0x80);
 				}