Regards
Shashank
On 7/1/2015 6:26 PM, Daniel Vetter wrote:
On Tue, Jun 30, 2015 at 09:49:57PM +0530, Shashank Sharma wrote:
Userspace always sets force. Are you sure this actually improves anything?
Yes we do. We have had this code for commercial projects, and that's really
important to have proper interrupt handling as well as to avoid race
condition between multiple HDMI detects from interrupt handler and
userspace detect calls. This is a must for HDMI compliance also.
There's no race, we have locks for this. And we already have a little bit
of edid caching, and you're code won't add more caching for the force =
true case. Which is why I wondered whether you've really seen improvements
with this on latest upstream, and not just an older android tree.
This caching is not useful, as in every detect call, we are doing a
unset EDID, and doing a set EDID again. The actual reason behind
multiple HDMI EDID reads is detect() getting called from user space
only.So every time there is a detect call, there is HDMI EDID read.
We should read EDID only on hotplug, cache it, and reuse it until hot
unplug.
Actually the plan is to use this force for GEN < 6 HW only, where the
hotplug doesn't work reliably (I remember our last conversation on some old
HW which doesn't support HPD properly). For vlv+, we can (will) use only
the cached EDID.
Ok, once more: HDMI hpd is unreliable everywhere. I have a gen7 here which
is half-busted it seems, and we've found examples for every single
platform that supports hdmi out there. The problem isn't necessarily spec
compliant HDMI sinks, but all the other crap ppl like to plug in.
Yes this means we'll not be spec compliant, but if we have reality vs.
spec, reality wins. At least in upstream.
We have tested HPD with several HDMI monitors for VLV, CHV SKL and now
for BXT also. We are getting reliable hotplugs and unplugs across these
platforms, with accurate information on long/short pulses. Can you
please give some details about what is your observation ?
Its very important for the Android projects to comply with the spec due
to certification pressure from customers. And we can get a common path
for us, if we know what exactly is the problem. But for sure we cant
ignore this factor that compliance is essential.
Also the goal should be to keep things cache for a few calls from
userspace (since often it pokes a few times in a row unfortuantely), for
which we need a proper timeout to clear the edid again.
Can you please let us know why ? Why do we need to clear this EDID caching
? We should clear it only in the next hot-unplug, and maintain this cached
EDID for all userspace detect operations. I believe as long as we have the
state machine maintained, we need not to clear it.
hotplug is not reliable, at least not outside of labs and validation
testers. And your code here throws the cached edid away every time force =
true is set, which is pretty much always. At least on upstream.
The only place where we don't set force is in the poll worker, and that's
only run when we have a hpd storm.
-Daniel
The new code doesn't throw away cached EDID for platform's > GEN6
but the current code does that, in every detect call.
The current state machine is:
=============================
1. Hotplug -> Unset EDID, Read EDID, Set edid
2. all detect calls -> Unset EDID, read EDID, Set EDID
3. Hotunplug -> Unset EDID
The state machine I am suggesting is:
=====================================
1. Hotplug -> throw away cached EDID, cache new one probing DDC
2. all detect() calls ->
use cached EDID only
3. hot unplug -> throw away cached EDID,
OR if you want to support some old platforms:
=============================================
1. Hotplug -> throw away cached EDID, cache new one probing DDC
2. all detect() calls -> (Support old HW with unstable HPD)
if (gen > GEN6)
use cached EDID only
else
probe DDC and read EDID, update cache
3. hot unplug -> throw away cached EDID,
-Daniel
Regards
Shashank
On Tue, Jun 30, 2015 at 4:36 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:
On Tue, Jun 30, 2015 at 11:13:58AM +0530, Sonika Jindal wrote:
From: Shashank Sharma <contactshashanksharma@xxxxxxxxx>
This patch makes sure that the HDMI detect function
reads EDID only when its forced to do it. All the other
times, it uses the connector->detect_edid which was cached
during hotplug handling in the hdmi_probe() function. As the
probe function gets called before detect in the interrupt handler
and handles the EDID cacheing part, its absolutely safe to assume
that presence of EDID reflects monitor connected and viceversa.
This will save us from many race conditions between hotplug/unplug
detect call handler threads and userspace calls for the same.
The previous patch in this patch series explains this in detail.
Signed-off-by: Shashank Sharma <contactshashanksharma@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_hdmi.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c
b/drivers/gpu/drm/i915/intel_hdmi.c
index 064ddd8..1fb6919 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1362,19 +1362,33 @@ static enum drm_connector_status
intel_hdmi_detect(struct drm_connector *connector, bool force)
{
enum drm_connector_status status;
+ struct intel_connector *intel_connector =
+ to_intel_connector(connector);
DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
connector->base.id, connector->name);
+ /*
+ * There are many userspace calls which probe EDID from
+ * detect path. In case on multiple hotplug/unplug, these
+ * can cause race conditions while probing EDID. Also its
+ * waste of CPU cycles to read the EDID again and again
+ * unless there is a real hotplug.
+ * So until we are forced, check connector status
+ * based on availability of cached EDID. This will avoid many of
+ * these race conditions and timing problems.
+ */
+ if (force)
Userspace always sets force. Are you sure this actually improves anything?
Also the goal should be to keep things cache for a few calls from
userspace (since often it pokes a few times in a row unfortuantely), for
which we need a proper timeout to clear the edid again.
-Daniel
+ intel_hdmi_probe(intel_connector->encoder);
- intel_hdmi_unset_edid(connector);
-
- if (intel_hdmi_set_edid(connector)) {
+ if (intel_connector->detect_edid) {
struct intel_hdmi *intel_hdmi =
intel_attached_hdmi(connector);
-
- hdmi_to_dig_port(intel_hdmi)->base.type =
INTEL_OUTPUT_HDMI;
status = connector_status_connected;
- } else
+ hdmi_to_dig_port(intel_hdmi)->base.type =
INTEL_OUTPUT_HDMI;
+ DRM_DEBUG_DRIVER("hdmi status = connected\n");
+ } else {
status = connector_status_disconnected;
+ DRM_DEBUG_DRIVER("hdmi status = disconnected\n");
+ }
return status;
}
--
1.7.10.4
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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