linux-kernel - [PATCH] drm/vc4: Fix sleeps during the IRQ handler for DSI transactions.

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Message-Id: <20170817210455.17885-1-eric@anholt.net>
Date:   Thu, 17 Aug 2017 14:04:55 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>
Subject: [PATCH] drm/vc4: Fix sleeps during the IRQ handler for DSI transactions.

VC4's DSI1 has a bug where the AXI connection is broken for 32-bit
writes from the CPU, so we use the DMA engine to DMA 32-bit values
into registers instead.  That sleeps, so we can't do it from the top
half.

As a solution (suggested by Arnd), we can mask the IRQ in the irqchip
in the top half, and re-enable it from an irqthread.

Signed-off-by: Eric Anholt <eric@...olt.net>
---
 drivers/gpu/drm/vc4/vc4_dsi.c | 39 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index ec1d646b3151..9556236b67d0 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -516,6 +516,8 @@ struct vc4_dsi {
 	/* Whether we're on bcm2835's DSI0 or DSI1. */
 	int port;
 
+	int irq;
+
 	/* DSI channel for the panel we're connected to. */
 	u32 channel;
 	u32 lanes;
@@ -1360,6 +1362,28 @@ static void dsi_handle_error(struct vc4_dsi *dsi,
 	*ret = IRQ_HANDLED;
 }
 
+/* Initial handler for port 1 where we need the reg_dma workaround.
+ * The register DMA writes sleep, so we can't do it in the top half.
+ * Instead we just disable the interrupt in the only way we have
+ * available (mask it in the irqchip), and continue on to the threaded
+ * handler.
+ */
+static irqreturn_t vc4_dsi_irq_defer_to_thread_handler(int irq, void *data)
+{
+	struct vc4_dsi *dsi = data;
+	u32 stat = DSI_PORT_READ(INT_STAT);
+
+	if (!stat)
+		return IRQ_NONE;
+
+	disable_irq_nosync(dsi->irq);
+
+	return IRQ_WAKE_THREAD;
+}
+
+/* Normal IRQ handler for port 0, or the threaded IRQ handler for port
+ * 1 where we need the reg_dma workaround.
+ */
 static irqreturn_t vc4_dsi_irq_handler(int irq, void *data)
 {
 	struct vc4_dsi *dsi = data;
@@ -1368,6 +1392,9 @@ static irqreturn_t vc4_dsi_irq_handler(int irq, void *data)
 
 	DSI_PORT_WRITE(INT_STAT, stat);
 
+	if (dsi->reg_dma_mem)
+		enable_irq(dsi->irq);
+
 	dsi_handle_error(dsi, &ret, stat,
 			 DSI1_INT_ERR_SYNC_ESC, "LPDT sync");
 	dsi_handle_error(dsi, &ret, stat,
@@ -1539,8 +1566,16 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
 	/* Clear any existing interrupt state. */
 	DSI_PORT_WRITE(INT_STAT, DSI_PORT_READ(INT_STAT));
 
-	ret = devm_request_irq(dev, platform_get_irq(pdev, 0),
-			       vc4_dsi_irq_handler, 0, "vc4 dsi", dsi);
+	dsi->irq = platform_get_irq(pdev, 0);
+	if (dsi->reg_dma_mem) {
+		ret = devm_request_threaded_irq(dev, dsi->irq,
+						vc4_dsi_irq_defer_to_thread_handler,
+						vc4_dsi_irq_handler, 0,
+						"vc4 dsi", dsi);
+	} else {
+		ret = devm_request_irq(dev, dsi->irq,
+				       vc4_dsi_irq_handler, 0, "vc4 dsi", dsi);
+	}
 	if (ret) {
 		if (ret != -EPROBE_DEFER)
 			dev_err(dev, "Failed to get interrupt: %d\n", ret);
-- 
2.14.1