[PATCH v2 2/3] media: sun4i-csi: disable interrupts when stopping streaming

[Cong Nguyen]

sun4i_csi_start_streaming() enables the frame-done interrupt in
CSI_INT_EN_REG, but sun4i_csi_stop_streaming() only stops the capture
engine (CSI_CPT_CTRL_REG) via sun4i_csi_capture_stop(). It never disables
the interrupt source nor synchronizes with the handler.

Capture stops at the end of the current frame, so a frame-done interrupt
can still fire shortly after stop_streaming() returns. If userspace then
closes the device, sun4i_csi_release() calls pm_runtime_put() and the CSI
block is powered down (clocks gated, reset asserted). A delayed interrupt
handler would then read/write CSI registers on the gated block, which can
hang or crash the system.

Add a helper that clears CSI_INT_EN_REG, reads it back to flush the posted
write, and calls synchronize_irq(), so no handler can run past that point.
Call it from stop_streaming() before returning the active buffers and
freeing the scratch buffer.

The start_streaming() error path (err_disable_device) has the same
problem: the frame-done interrupt is enabled and capture is started
before the s_stream call that can fail, so a handler can run while the
error path frees the scratch buffer and returns the queued buffers.
Apply the same teardown there. Store the IRQ number in struct sun4i_csi
so it is available in both paths.

Fixes: 577bbf23b758 ("media: sunxi: Add A10 CSI driver")
Cc: stable at vger.kernel.org
Assisted-by: Claude:claude-opus-4
Signed-off-by: Cong Nguyen <congnt264 at gmail.com>
---
 .../platform/sunxi/sun4i-csi/sun4i_csi.h      |  1 +
 .../platform/sunxi/sun4i-csi/sun4i_dma.c      | 20 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/media/platform/sunxi/sun4i-csi/sun4i_csi.h b/drivers/media/platform/sunxi/sun4i-csi/sun4i_csi.h
index 4e0c2df45d4d..51173faea871 100644
--- a/drivers/media/platform/sunxi/sun4i-csi/sun4i_csi.h
+++ b/drivers/media/platform/sunxi/sun4i-csi/sun4i_csi.h
@@ -112,6 +112,7 @@ struct sun4i_csi {
 	const struct sun4i_csi_traits	*traits;
 
 	void __iomem			*regs;
+	int				irq;
 	struct clk			*bus_clk;
 	struct clk			*isp_clk;
 	struct clk			*ram_clk;
diff --git a/drivers/media/platform/sunxi/sun4i-csi/sun4i_dma.c b/drivers/media/platform/sunxi/sun4i-csi/sun4i_dma.c
index e911c7f7acc5..fd83dbd1a3ff 100644
--- a/drivers/media/platform/sunxi/sun4i-csi/sun4i_dma.c
+++ b/drivers/media/platform/sunxi/sun4i-csi/sun4i_dma.c
@@ -43,6 +43,23 @@ static void sun4i_csi_capture_stop(struct sun4i_csi *csi)
 	writel(0, csi->regs + CSI_CPT_CTRL_REG);
 }
 
+static void sun4i_csi_disable_irq(struct sun4i_csi *csi)
+{
+	/*
+	 * Disable the frame done interrupt and wait for the handler to
+	 * finish. A frame may complete right as capture is stopped, so an
+	 * interrupt can still be pending here; without this the handler could
+	 * run after the device is powered down (pm_runtime_put() on release)
+	 * and access registers on a gated block.
+	 *
+	 * Read the register back to flush the posted write so the disable has
+	 * reached the device before synchronize_irq() waits for the handler.
+	 */
+	writel(0, csi->regs + CSI_INT_EN_REG);
+	readl(csi->regs + CSI_INT_EN_REG);
+	synchronize_irq(csi->irq);
+}
+
 static int sun4i_csi_queue_setup(struct vb2_queue *vq,
 				 unsigned int *nbuffers,
 				 unsigned int *nplanes,
@@ -328,6 +345,7 @@ static int sun4i_csi_start_streaming(struct vb2_queue *vq, unsigned int count)
 
 err_disable_device:
 	sun4i_csi_capture_stop(csi);
+	sun4i_csi_disable_irq(csi);
 
 err_disable_pipeline:
 	video_device_pipeline_stop(&csi->vdev);
@@ -353,6 +371,7 @@ static void sun4i_csi_stop_streaming(struct vb2_queue *vq)
 
 	v4l2_subdev_call(csi->src_subdev, video, s_stream, 0);
 	sun4i_csi_capture_stop(csi);
+	sun4i_csi_disable_irq(csi);
 
 	/* Release all active buffers */
 	spin_lock_irqsave(&csi->qlock, flags);
@@ -438,6 +457,7 @@ int sun4i_csi_dma_register(struct sun4i_csi *csi, int irq)
 		dev_err(csi->dev, "Couldn't register our interrupt\n");
 		goto err_unregister_device;
 	}
+	csi->irq = irq;
 
 	return 0;
 
-- 
2.25.1