linux-kernel - [PATCH 1/3] platform/x86: intel_scu_ipc: Check status after timeouts in busy

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Message-ID: <20230831011405.3246849-2-swboyd@chromium.org>
Date:   Wed, 30 Aug 2023 18:14:01 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        platform-driver-x86@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Prashant Malani <pmalani@...omium.org>
Subject: [PATCH 1/3] platform/x86: intel_scu_ipc: Check status after timeouts in busy_loop()

It's possible for the polling loop in busy_loop() to get scheduled away
for a long time.

  status = ipc_read_status(scu);
  <long time scheduled away>
  if (!(status & IPC_STATUS_BUSY))

If this happens, then the status bit could change and this function
would never test it again after checking the jiffies against the timeout
limit. Polling code should check the condition one more time after the
timeout in case this happens.

The read_poll_timeout() helper implements this logic, and is shorter, so
simply use that helper here.

Cc: Prashant Malani <pmalani@...omium.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Fixes: e7b7ab3847c9 ("platform/x86: intel_scu_ipc: Sleeping is fine when polling")
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/platform/x86/intel_scu_ipc.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/platform/x86/intel_scu_ipc.c b/drivers/platform/x86/intel_scu_ipc.c
index 6851d10d6582..5a37becc65aa 100644
--- a/drivers/platform/x86/intel_scu_ipc.c
+++ b/drivers/platform/x86/intel_scu_ipc.c
@@ -19,6 +19,7 @@
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 
@@ -231,19 +232,15 @@ static inline u32 ipc_data_readl(struct intel_scu_ipc_dev *scu, u32 offset)
 /* Wait till scu status is busy */
 static inline int busy_loop(struct intel_scu_ipc_dev *scu)
 {
-	unsigned long end = jiffies + IPC_TIMEOUT;
-
-	do {
-		u32 status;
-
-		status = ipc_read_status(scu);
-		if (!(status & IPC_STATUS_BUSY))
-			return (status & IPC_STATUS_ERR) ? -EIO : 0;
+	u8 status;
+	int err;
 
-		usleep_range(50, 100);
-	} while (time_before(jiffies, end));
+	err = read_poll_timeout(ipc_read_status, status, !(status & IPC_STATUS_BUSY),
+				100, jiffies_to_usecs(IPC_TIMEOUT), false, scu);
+	if (err)
+		return err;
 
-	return -ETIMEDOUT;
+	return (status & IPC_STATUS_ERR) ? -EIO : 0;
 }
 
 /* Wait till ipc ioc interrupt is received or timeout in 10 HZ */
-- 
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