linux-kernel - [PATCH v4 2/4] spi: cadence-qspi: remove system-wide suspend helper calls from runtime PM hooks

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Message-Id: <20240222-cdns-qspi-pm-fix-v4-2-6b6af8bcbf59@bootlin.com>
Date: Thu, 22 Feb 2024 11:12:30 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: Mark Brown <broonie@...nel.org>, Apurva Nandan <a-nandan@...com>, 
 Dhruva Gole <d-gole@...com>
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>
Subject: [PATCH v4 2/4] spi: cadence-qspi: remove system-wide suspend
 helper calls from runtime PM hooks

The ->runtime_suspend() and ->runtime_resume() callbacks are not
expected to call spi_controller_suspend() and spi_controller_resume().
Remove calls to those in the cadence-qspi driver.

Those helpers have two roles currently:
 - They stop/start the queue, including dealing with the kworker.
 - They toggle the SPI controller SPI_CONTROLLER_SUSPENDED flag. It
   requires acquiring ctlr->bus_lock_mutex.

Step one is irrelevant because cadence-qspi is not queued. Step two
however has two implications:
 - A deadlock occurs, because ->runtime_resume() is called in a context
   where the lock is already taken (in the ->exec_op() callback, where
   the usage count is incremented).
 - It would disallow all operations once the device is auto-suspended.

Here is a brief call tree highlighting the mutex deadlock:

spi_mem_exec_op()
        ...
        spi_mem_access_start()
                mutex_lock(&ctlr->bus_lock_mutex)

        cqspi_exec_mem_op()
                pm_runtime_resume_and_get()
                        cqspi_resume()
                                spi_controller_resume()
                                        mutex_lock(&ctlr->bus_lock_mutex)
                ...

        spi_mem_access_end()
                mutex_unlock(&ctlr->bus_lock_mutex)
        ...

Fixes: 0578a6dbfe75 ("spi: spi-cadence-quadspi: add runtime pm support")
Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
---
 drivers/spi/spi-cadence-quadspi.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index d19ba024c80b..809bbbb876ad 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -1930,14 +1930,10 @@ static void cqspi_remove(struct platform_device *pdev)
 static int cqspi_suspend(struct device *dev)
 {
 	struct cqspi_st *cqspi = dev_get_drvdata(dev);
-	int ret;
 
-	ret = spi_controller_suspend(cqspi->host);
 	cqspi_controller_enable(cqspi, 0);
-
 	clk_disable_unprepare(cqspi->clk);
-
-	return ret;
+	return 0;
 }
 
 static int cqspi_resume(struct device *dev)
@@ -1950,8 +1946,7 @@ static int cqspi_resume(struct device *dev)
 
 	cqspi->current_cs = -1;
 	cqspi->sclk = 0;
-
-	return spi_controller_resume(cqspi->host);
+	return 0;
 }
 
 static DEFINE_RUNTIME_DEV_PM_OPS(cqspi_dev_pm_ops, cqspi_suspend,

-- 
2.43.2