linux-kernel - [PATCH v3 2/4] platform/x86: intel_scu_ipc: Check status upon timeout in ipc_wait_for

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Message-ID: <20230911193937.302552-3-swboyd@chromium.org>
Date:   Mon, 11 Sep 2023 12:39:34 -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 v3 2/4] platform/x86: intel_scu_ipc: Check status upon timeout in ipc_wait_for_interrupt()

It's possible for the completion in ipc_wait_for_interrupt() to timeout,
simply because the interrupt was delayed in being processed. A timeout
in itself is not an error. This driver should check the status register
upon a timeout to ensure that scheduling or interrupt processing delays
don't affect the outcome of the IPC return value.

 CPU0                                                   SCU
 ----                                                   ---
 ipc_wait_for_interrupt()
  wait_for_completion_timeout(&scu->cmd_complete)
  [TIMEOUT]                                             status[IPC_STATUS_BUSY]=0

Fix this problem by reading the status bit in all cases, regardless of
the timeout. If the completion times out, we'll assume the problem was
that the IPC_STATUS_BUSY bit was still set, but if the status bit is
cleared in the meantime we know that we hit some scheduling delay and we
should just check the error bit.

Cc: Prashant Malani <pmalani@...omium.org>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Fixes: ed12f295bfd5 ("ipc: Added support for IPC interrupt mode")
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/platform/x86/intel_scu_ipc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/intel_scu_ipc.c b/drivers/platform/x86/intel_scu_ipc.c
index 5a37becc65aa..8be1686e22e9 100644
--- a/drivers/platform/x86/intel_scu_ipc.c
+++ b/drivers/platform/x86/intel_scu_ipc.c
@@ -248,10 +248,12 @@ static inline int ipc_wait_for_interrupt(struct intel_scu_ipc_dev *scu)
 {
 	int status;
 
-	if (!wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT))
-		return -ETIMEDOUT;
+	wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT);
 
 	status = ipc_read_status(scu);
+	if (status & IPC_STATUS_BUSY)
+		return -ETIMEDOUT;
+
 	if (status & IPC_STATUS_ERR)
 		return -EIO;
 
-- 
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