Change in coreboot[master]: Revert "Revert "drivers/intel/fsp2_0: Allow `mp_startup_all_cpus()` t...

[Nick Vaccaro (Code Review)]

Nick Vaccaro has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/62907 )

Change subject: Revert "Revert "drivers/intel/fsp2_0: Allow `mp_startup_all_cpus()` to run serially""
......................................................................

Revert "Revert "drivers/intel/fsp2_0: Allow `mp_startup_all_cpus()` to run serially""

This reverts a change that was causing hangs and exceptions during boot
on an ADL brya4es.

This reverts commit 40ca79714ad7d5f2aa201d83db4d97f21260d924.

BUG=b:224873032
TEST=`emerge-brya coreboot chromeos-bootimage`, flash and verify brya4es
is able so successfully reboot 50 times without any issues.

Change-Id: I88c15a51c5d27fbd243478c923e75962d3f8d67d
Signed-off-by: Nick Vaccaro 
---
M src/drivers/intel/fsp2_0/ppi/mp_service_ppi.c
1 file changed, 17 insertions(+), 4 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/07/62907/1

diff --git a/src/drivers/intel/fsp2_0/ppi/mp_service_ppi.c b/src/drivers/intel/fsp2_0/ppi/mp_service_ppi.c
index 50e35b0..9aef1b6 100644
--- a/src/drivers/intel/fsp2_0/ppi/mp_service_ppi.c
+++ b/src/drivers/intel/fsp2_0/ppi/mp_service_ppi.c
@@ -94,10 +94,23 @@
    /* Run on BSP */
    procedure(argument);

-	/* Run on APs */
-	if (mp_run_on_aps((void *)procedure, argument,
-			MP_RUN_ON_ALL_CPUS, timeout_usec) != CB_SUCCESS) {
-		printk(BIOS_ERR, "%s: Exit with Failure\n", __func__);
+	/*
+	 * Run on APs Serially
+	 *
+	 * FIXME: As per MP service specification, EDK2 is allowed to specify the mode
+	 * in which a 'func' routine should be executed on APs (i.e. execute serially
+	 * or concurrently).
+	 *
+	 * MP service API `StartupAllCPUs` doesn't specify such requirement.
+	 * Hence, running the `CpuCacheInfoCollectCoreAndCacheData`
+	 * (UefiCpuPkg/Library/CpuCacheInfoLib/CpuCacheInfoLib.c#194)
+	 * simultaneously on APs results in a coherency issue (hang while executing `func`)
+	 * due to lack of acquiring a spin lock while accessing common data structure in
+	 * multiprocessor environment.
+	 */
+	if (mp_run_on_all_aps((void *)procedure, argument, timeout_usec, false) !=
+				CB_SUCCESS) {
+		printk(BIOS_DEBUG, "%s: Exit with Failure\n", __func__);
    	return FSP_NOT_STARTED;
    }