Patch "ACPI: PCC: replace wait_for_completion()" has been added to the 6.0-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ACPI: PCC: replace wait_for_completion()

to the 6.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     acpi-pcc-replace-wait_for_completion.patch
and it can be found in the queue-6.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 07e87c80aa91e3d0e14983a7b699eacf6e62c522
Author: Huisong Li <lihuisong@xxxxxxxxxx>
Date:   Tue Sep 20 17:44:59 2022 +0800

    ACPI: PCC: replace wait_for_completion()
    
    [ Upstream commit 91cefefb699120efd0a5ba345d12626b688f86ce ]
    
    Currently, the function waiting for completion of mailbox operation is
    'wait_for_completion()'.  The PCC method will be permanently blocked if
    this mailbox message fails to execute. So this patch replaces it with
    'wait_for_completion_timeout()'. And set the timeout interval to an
    arbitrary retries on top of nominal to prevent the remote processor is
    slow to respond to PCC commands.
    
    Fixes: 77e2a04745ff ("ACPI: PCC: Implement OperationRegion handler for the PCC Type 3 subtype")
    Signed-off-by: Huisong Li <lihuisong@xxxxxxxxxx>
    Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/acpi/acpi_pcc.c b/drivers/acpi/acpi_pcc.c
index 84f1ac416b57..16ba875e3293 100644
--- a/drivers/acpi/acpi_pcc.c
+++ b/drivers/acpi/acpi_pcc.c
@@ -23,6 +23,12 @@
 
 #include <acpi/pcc.h>
 
+/*
+ * Arbitrary retries in case the remote processor is slow to respond
+ * to PCC commands
+ */
+#define PCC_CMD_WAIT_RETRIES_NUM	500
+
 struct pcc_data {
 	struct pcc_mbox_chan *pcc_chan;
 	void __iomem *pcc_comm_addr;
@@ -89,6 +95,7 @@ acpi_pcc_address_space_handler(u32 function, acpi_physical_address addr,
 {
 	int ret;
 	struct pcc_data *data = region_context;
+	u64 usecs_lat;
 
 	reinit_completion(&data->done);
 
@@ -99,8 +106,20 @@ acpi_pcc_address_space_handler(u32 function, acpi_physical_address addr,
 	if (ret < 0)
 		return AE_ERROR;
 
-	if (data->pcc_chan->mchan->mbox->txdone_irq)
-		wait_for_completion(&data->done);
+	if (data->pcc_chan->mchan->mbox->txdone_irq) {
+		/*
+		 * pcc_chan->latency is just a Nominal value. In reality the remote
+		 * processor could be much slower to reply. So add an arbitrary
+		 * amount of wait on top of Nominal.
+		 */
+		usecs_lat = PCC_CMD_WAIT_RETRIES_NUM * data->pcc_chan->latency;
+		ret = wait_for_completion_timeout(&data->done,
+						  usecs_to_jiffies(usecs_lat));
+		if (ret == 0) {
+			pr_err("PCC command executed timeout!\n");
+			return AE_TIME;
+		}
+	}
 
 	mbox_client_txdone(data->pcc_chan->mchan, ret);