[PATCH v15 3/7] spi: pxa2xx: overhaul teardown and suspend sequence using pxa2xx_spi_off

[Shih-Yuan Lee <fourdollars@debian.org>]

When removing the driver or suspending the device, the clock must not
be disabled while shared interrupts are still active. Gating the clock
before waiting for in-flight interrupt handlers to complete results
in race conditions where the handler performs unclocked MMIO accesses,
causing PCIe Completion Timeouts.

Overhaul the remove, suspend, and runtime_suspend paths to use a strict
synchronized teardown order:
1. Disable hardware interrupt generation at the controller level.
2. Mark the device state as suspended (suspended = true) to prevent
   subsequent interrupt handlers from attempting MMIO reads.
3. Call synchronize_irq() to wait for any active interrupt handlers
   to drain completely.
4. Gate the clock via pxa2xx_spi_clk_disable().

Additionally, commit 29d7e05c5f75 ("spi: pxa2xx: Avoid touching
SSCR0_SSE on MMP2") documented that disabling the hardware block via SSE on
MMP2 SoC platforms corrupts the RX/TX FIFO. Instead of calling
pxa_ssp_disable() directly, use the helper function pxa2xx_spi_off(),
which respects the MMP2 platform quirk by bypassing SSE register writes.

Signed-off-by: Shih-Yuan Lee <fourdollars@debian.org>
---
 drivers/spi/spi-pxa2xx.c | 49 ++++++++++++++++++++++++++++++++--------
 1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index d4a9a48c2624..64b5ec744756 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -1495,16 +1495,24 @@ void pxa2xx_spi_remove(struct device *dev)
 
 	spi_unregister_controller(drv_data->controller);
 
-	/* Disable the SSP at the peripheral and SOC level */
-	pxa_ssp_disable(ssp);
+	/* Disable SSP interrupt generation on hardware level while clock is active */
+	pxa2xx_spi_off(drv_data);
+
+	/* Mark as suspended to prevent further IRQ handling */
+	drv_data->suspended = true;
+
+	/* Wait for any pending interrupt handlers to complete */
+	synchronize_irq(ssp->irq);
+
+	/* Release IRQ */
+	free_irq(ssp->irq, drv_data);
+
+	/* Safe to disable the SSP clock now */
 	pxa2xx_spi_clk_disable(drv_data);
 
 	/* Release DMA */
 	if (drv_data->controller_info->enable_dma)
 		pxa2xx_spi_dma_release(drv_data);
-
-	/* Release IRQ */
-	free_irq(ssp->irq, drv_data);
 }
 EXPORT_SYMBOL_NS_GPL(pxa2xx_spi_remove, "SPI_PXA2xx");
 
@@ -1518,10 +1526,11 @@ static int pxa2xx_spi_suspend(struct device *dev)
 	if (status)
 		return status;
 
-	pxa_ssp_disable(ssp);
+	pxa2xx_spi_off(drv_data);
+	drv_data->suspended = true;
+	synchronize_irq(ssp->irq);
 
-	if (!pm_runtime_suspended(dev))
-		pxa2xx_spi_clk_disable(drv_data);
+	pxa2xx_spi_clk_disable(drv_data);
 
 	return 0;
 }
@@ -1529,6 +1538,7 @@ static int pxa2xx_spi_suspend(struct device *dev)
 static int pxa2xx_spi_resume(struct device *dev)
 {
 	struct driver_data *drv_data = dev_get_drvdata(dev);
+	struct ssp_device *ssp = drv_data->ssp;
 	int status;
 
 	/* Enable the SSP clock */
@@ -1538,14 +1548,27 @@ static int pxa2xx_spi_resume(struct device *dev)
 			return status;
 	}
 
+	drv_data->suspended = false;
+
 	/* Start the queue running */
-	return spi_controller_resume(drv_data->controller);
+	status = spi_controller_resume(drv_data->controller);
+	if (status) {
+		drv_data->suspended = true;
+		synchronize_irq(ssp->irq);
+		pxa2xx_spi_clk_disable(drv_data);
+		return status;
+	}
+
+	return 0;
 }
 
 static int pxa2xx_spi_runtime_suspend(struct device *dev)
 {
 	struct driver_data *drv_data = dev_get_drvdata(dev);
 
+	pxa2xx_spi_off(drv_data);
+	drv_data->suspended = true;
+	synchronize_irq(drv_data->ssp->irq);
 	pxa2xx_spi_clk_disable(drv_data);
 	return 0;
 }
@@ -1553,8 +1576,14 @@ static int pxa2xx_spi_runtime_suspend(struct device *dev)
 static int pxa2xx_spi_runtime_resume(struct device *dev)
 {
 	struct driver_data *drv_data = dev_get_drvdata(dev);
+	int status;
+
+	status = pxa2xx_spi_clk_enable(drv_data);
+	if (status)
+		return status;
 
-	return pxa2xx_spi_clk_enable(drv_data);
+	drv_data->suspended = false;
+	return 0;
 }
 
 EXPORT_NS_GPL_DEV_PM_OPS(pxa2xx_spi_pm_ops, SPI_PXA2xx) = {
-- 
2.39.5