On Thu, 17 Aug 2017 14:04:55 -0700 Eric Anholt eric@anholt.net wrote:

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@anholt.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);

Are you sure you need to explicitly disable the IRQ here? Did you try with an IRQF_ONESHOT flag when registering your irq handler (this should do exactly what you're doing here: mask the interrupt until the threaded handler returns IRQ_DONE or IRQ_NONE [1])?

[1]http://elixir.free-electrons.com/linux/v4.3.2/source/include/linux/interrupt...

• 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);