[PATCH v16 4/7] spi: pxa2xx: lock out runtime autosuspend for Intel LPSS SPI in PIO mode

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

When operating in PIO mode on Intel LPSS SPI controllers, runtime PM
autosuspend clock-gates the hardware block when idle. On subsequent
transfers, MMIO accesses to trigger resume are performed before the runtime
PM state machine can wake the controller, causing PCIe Completion Timeouts.
This issue does not affect DMA mode, where the DMA engine holds the required
resources, nor does it affect non-LPSS controllers.

Lock out runtime PM autosuspend for LPSS SPI controllers specifically
when operating in PIO mode.

Acquire a runtime PM reference via pm_runtime_get_noresume() in
pxa2xx_spi_probe() after registration, and release it via
pm_runtime_put_noidle() in pxa2xx_spi_remove() before hardware teardown to
ensure the runtime PM reference held in probe is released without invoking
runtime_suspend on already-unclocked hardware.

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

diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
index 6bfd3382acc3..34241a6742eb 100644
--- a/drivers/spi/spi-pxa2xx.c
+++ b/drivers/spi/spi-pxa2xx.c
@@ -1473,6 +1473,9 @@ int pxa2xx_spi_probe(struct device *dev, struct ssp_device *ssp,
 		goto out_error_irq_alloc;
 	}
 
+	if (is_lpss_ssp(drv_data) && !platform_info->enable_dma)
+		pm_runtime_get_noresume(dev);
+
 	return status;
 
 out_error_irq_alloc:
@@ -1495,6 +1498,13 @@ void pxa2xx_spi_remove(struct device *dev)
 
 	spi_unregister_controller(drv_data->controller);
 
+	/* Release the PM reference held in probe for LPSS PIO mode before
+	 * hardware teardown so the PM core does not invoke runtime_suspend
+	 * on already-unclocked hardware.
+	 */
+	if (is_lpss_ssp(drv_data) && !drv_data->controller_info->enable_dma)
+		pm_runtime_put_noidle(dev);
+
 	/* Disable SSP interrupt generation on hardware level while clock is active */
 	pxa2xx_spi_off(drv_data);
 
-- 
2.39.5