Re: [RFC 06/14] drm/i915: Disable vlank interrupt for disabling MIPI cmd mode

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jun 16, 2015 at 10:24:57PM +0530, Singh, Gaurav K wrote:
> 
> 
> On 5/29/2015 10:53 PM, Daniel Vetter wrote:
> >On Fri, May 29, 2015 at 07:14:43PM +0200, Daniel Vetter wrote:
> >>On Fri, May 29, 2015 at 04:06:58PM +0530, Gaurav K Singh wrote:
> >>>vblank interrupt should be disabled before starting the disable
> >>>sequence for MIPI command mode. Otherwise when pipe is disabled
> >>>TE interurpt will be still handled and one memory write command
> >>>will be sent with pipe disabled. This makes the pipe hw to get
> >>>stuck and it doesn't recover in the next enable sequence causing
> >>>display blank out.
> >>>
> >>>Signed-off-by: Yogesh Mohan Marimuthu <yogesh.mohan.marimuthu@intel.com>
> >>>Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
> >>>---
> >>>  drivers/gpu/drm/i915/intel_dsi.c |   14 ++++++++++++++
> >>>  1 file changed, 14 insertions(+)
> >>>
> >>>diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
> >>>index 04d8ce0..aeea289 100644
> >>>--- a/drivers/gpu/drm/i915/intel_dsi.c
> >>>+++ b/drivers/gpu/drm/i915/intel_dsi.c
> >>>@@ -513,11 +513,25 @@ static void intel_dsi_enable_nop(struct intel_encoder *encoder)
> >>>  static void intel_dsi_pre_disable(struct intel_encoder *encoder)
> >>>  {
> >>>+	struct drm_device *dev = encoder->base.dev;
> >>>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
> >>>+	struct intel_crtc *intel_crtc = to_intel_crtc(encoder->base.crtc);
> >>>+	int pipe = intel_crtc->pipe;
> >>>  	enum port port;
> >>>  	DRM_DEBUG_KMS("\n");
> >>>+	if (is_cmd_mode(intel_dsi)) {
> >>>+		dev->driver->disable_vblank(dev, pipe);
> >>>+
> >>>+		/*
> >>>+		 * Make sure that the last frame is sent otherwise pipe can get
> >>>+		 * stuck. Currently providing delay time for ~2 vblanks
> >>>+		 * assuming 60fps.
> >>>+		 */
> >>>+		mdelay(40);
> >>>+	}
> >>Nope. You need to move around the drm_vblank_off suitably, only that
> >>function correctly handles all the book-keeping around vblank interrupts.
> >>If this doesn't work out because of ordering we need to dig into this and
> >>figure out something. Worst case we need to push the drm_vblank_off call
> >>into encoder callbacks for everyone. That's something we already discussed
> >>but then decided against.
> >I seem to be blind, but where exactly is that vblank-driven upload code?

This question is still open for me. Why exactly do we have to disable
vblanks here already? I feel like this is hiding some deeper
synchronization issue - just disabling the vblank source doesn't mean they
have all be processed correctly by the irq handler. If this is really
required then you still have a big race here, even when using
drm_vblank_off.
-Daneil
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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