linux-kernel - [PATCH 1/2] ACPI: PCC: replace wait_for

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Date:   Tue, 20 Sep 2022 17:44:59 +0800
From:   Huisong Li <lihuisong@...wei.com>
To:     <linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <rafael@...nel.org>, <sudeep.holla@....com>,
        <rafael.j.wysocki@...el.com>, <wanghuiqiang@...wei.com>,
        <huangdaode@...wei.com>, <lihuisong@...wei.com>
Subject: [PATCH 1/2] ACPI: PCC: replace wait_for_completion()

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@...wei.com>
---
 drivers/acpi/acpi_pcc.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_pcc.c b/drivers/acpi/acpi_pcc.c
index a12b55d81209..a1052fe998bf 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;
@@ -86,6 +92,7 @@ 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);
 
@@ -96,8 +103,20 @@ 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);
 
-- 
2.33.0