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, use an interrupt thread so that all our writes happen
when sleeping is is allowed.

v2: Use IRQF_ONESHOT (suggested by Boris)
v3: Style nitpicks.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20171014001255.32005-1-eric@anholt.net
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com> (v2)

1 files changed, 30 insertions, 2 deletions

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index 554605af344e..94085f8bcd68 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -1360,6 +1360,27 @@ 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 use IRQF_ONESHOT so that the IRQ gets disabled in the
+ * parent interrupt contrller until our interrupt thread is done.
+ */
+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;
+
+        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;
@@ -1539,8 +1560,15 @@ 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);
+        if (dsi->reg_dma_mem)
+                ret = devm_request_threaded_irq(dev, platform_get_irq(pdev, 0),
+                                                vc4_dsi_irq_defer_to_thread_handler,
+                                                vc4_dsi_irq_handler,
+                                                IRQF_ONESHOT,
+                                                "vc4 dsi", dsi);
+        else
+                ret = devm_request_irq(dev, platform_get_irq(pdev, 0),
+                                       vc4_dsi_irq_handler, 0, "vc4 dsi", dsi);
         if (ret) {
                 if (ret != -EPROBE_DEFER)
                         dev_err(dev, "Failed to get interrupt: %d\n", ret);