[PATCH] platform/x86: ISST: Do Not Restore SST MSRs on CPU Online Operation

[PATCH] platform/x86: ISST: Do Not Restore SST MSRs on CPU Online Operation

[Srinivas Pandruvada]

During CPU offline/online operations, the hardware retains MSR settings.
Even if all CPUs are offlined, the package does not lose its MSR
settings.

Therefore, it is unnecessary to restore MSRs which are modified during
the online operation, and this extra step can be removed.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 .../intel/speed_select_if/isst_if_common.c    | 21 -------------------
 1 file changed, 21 deletions(-)

diff --git a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
index 31239a93dd71..3c4198ce17f2 100644
--- a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
+++ b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
@@ -198,25 +198,6 @@ void isst_resume_common(void)
 }
 EXPORT_SYMBOL_GPL(isst_resume_common);
 
-static void isst_restore_msr_local(int cpu)
-{
-	struct isst_cmd *sst_cmd;
-	int i;
-
-	mutex_lock(&isst_hash_lock);
-	for (i = 0; i < ARRAY_SIZE(punit_msr_white_list); ++i) {
-		if (!punit_msr_white_list[i])
-			break;
-
-		hash_for_each_possible(isst_hash, sst_cmd, hnode,
-				       punit_msr_white_list[i]) {
-			if (!sst_cmd->mbox_cmd_type && sst_cmd->cpu == cpu)
-				wrmsrl_safe(sst_cmd->cmd, sst_cmd->data);
-		}
-	}
-	mutex_unlock(&isst_hash_lock);
-}
-
 /**
  * isst_if_mbox_cmd_invalid() - Check invalid mailbox commands
  * @cmd: Pointer to the command structure to verify.
@@ -434,8 +415,6 @@ static int isst_if_cpu_online(unsigned int cpu)
 set_punit_id:
 	isst_cpu_info[cpu].punit_cpu_id = data;
 
-	isst_restore_msr_local(cpu);
-
 	return 0;
 }
 
-- 
2.49.0

Re: [PATCH] platform/x86: ISST: Do Not Restore SST MSRs on CPU Online Operation

[Ilpo Järvinen]

On Mon, 05 May 2025 13:27:22 -0700, Srinivas Pandruvada wrote:

> During CPU offline/online operations, the hardware retains MSR settings.
> Even if all CPUs are offlined, the package does not lose its MSR
> settings.
> 
> Therefore, it is unnecessary to restore MSRs which are modified during
> the online operation, and this extra step can be removed.
> 
> [...]


Thank you for your contribution, it has been applied to my local
review-ilpo-next branch. Note it will show up in the public
platform-drivers-x86/review-ilpo-next branch only once I've pushed my
local branch there, which might take a while.

The list of commits applied:
[1/1] platform/x86: ISST: Do Not Restore SST MSRs on CPU Online Operation
      commit: 68ea978fa096dd62aed386b384e3bc7e713d3b79

--
 i.