[Intel-gfx] [PATCH] drm/i915: storm detection documentation update

[Daniel Vetter]

On Thu, Jul 09, 2015 at 06:22:01PM +0530, Sivakumar Thulasimani wrote:
> 
> 
> On 7/8/2015 8:50 PM, Daniel Vetter wrote:
> >On Wed, Jul 08, 2015 at 06:54:06PM +0530, Sivakumar Thulasimani wrote:
> >>
> >>On 7/7/2015 5:01 PM, Daniel Vetter wrote:
> >>>On Tue, Jul 07, 2015 at 04:10:49PM +0530, Sivakumar Thulasimani wrote:
> >>>>From: "Thulasimani,Sivakumar" <sivakumar.thulasimani at intel.com>
> >>>>
> >>>>Update the hotplug documentation to explain that hotplug storm
> >>>>is not expected for Display port panels and hence is not handled
> >>>>in current code.
> >>>>
> >>>>Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani at intel.com>
> >>>>---
> >>>>  drivers/gpu/drm/i915/intel_hotplug.c |    4 ++++
> >>>>  1 file changed, 4 insertions(+)
> >>>>
> >>>>diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> >>>>index bac91a1..7dc5e6a 100644
> >>>>--- a/drivers/gpu/drm/i915/intel_hotplug.c
> >>>>+++ b/drivers/gpu/drm/i915/intel_hotplug.c
> >>>>@@ -66,6 +66,10 @@
> >>>>   * while before being re-enabled. The intention is to mitigate issues raising
> >>>>   * from broken hardware triggering massive amounts of interrupts and grinding
> >>>>   * the system to a halt.
> >>>>+ *
> >>>>+ * Hotplug interrupt storm is not expected on Display port panel, hence the
> >>>>+ * current code only handles disabling and later enabling of HPD interrupts
> >>>>+ * for HDMI panels through the storm handling set of functions.
> >>>This isn't accurate, we handle storms on everything _but_ DP (tv, vga,
> >>>sdvo, ...). I'd go with
> >>>
> >>>  * Hotplug interrupt storm is not expected on Display port panel, hence the
> >>>  * current code doesn't handle irq reenabling when a DP sink is connected
> >>>  * and the hpd is handled by the DP callbacks. But on DP+ ports
> >>>  * storms are still handled correctly in all other cases (e.g. due to HDMI
> >>>  * sinks).
> >>>
> >>>Could still be improved I think.
> >>>
> >>>-Daniel
> >>>
> >>Sorry i don't get the "DP+" reference here. By DP+, do you mean dongles ?
> >>passive dongles will report them selves as HDMI to respective detect
> >>routines
> >>active dongles will be still treated as DP hence not handling HPD will apply
> >>to any
> >>display connected through active dongle as well.
> >DP+ is DP with support for HDMI with level shifter cables (i.e. all the
> >ports on intel chips). I just wanted to make it clear that storm handling
> >doesn't work if we have a confirmed DP sink on the port, but will work in
> >any other cases (nothing or HDMI sink or DVI or whatever connected). Like
> >I said some room for improvement ;-)
> >-Daniel
> how about the following ?
> 
>  * current implementation expects that hotplug interrupt storm will not be

s/current/Current/

>  * seen when display port sink is connected, hence on platforms whose DP
>  * callback is handled by i915_digport_work_func reenabling of hpd is not
>  * performed ( it was never expected to be disabled in the first place ;) )
>  * this is specific to DP sinks handled by this routine and any other display
>  * such as HDMI or DVI enabled on the same port will have proper logic since
>  * it will use i915_hotplug_work_func where this logic is handled.

lgtm.
-Daniel

> 
> please provide any corrections or new comment to be used, i'll upload a new
> patch with
> the final approved text block.
> 
> -- 
> regards,
> Sivakumar
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch