On 2021-04-21 10:26, khsieh@xxxxxxxxxxxxxx wrote:
On 2021-04-20 15:01, Stephen Boyd wrote:
Quoting Kuogee Hsieh (2021-04-16 13:27:57)
Some dongle may generate more than one irq_hpd events in a short
period of
time. This patch will treat those irq_hpd events as single one and
service
only one irq_hpd event.
Why is it bad to get multiple irq_hpd events in a short period of
time?
Please tell us here in the commit text.
Signed-off-by: Kuogee Hsieh <khsieh@xxxxxxxxxxxxxx>
---
drivers/gpu/drm/msm/dp/dp_display.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/gpu/drm/msm/dp/dp_display.c
b/drivers/gpu/drm/msm/dp/dp_display.c
index 5a39da6..0a7d383 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -707,6 +707,9 @@ static int dp_irq_hpd_handle(struct
dp_display_private *dp, u32 data)
return 0;
}
+ /* only handle first irq_hpd in case of multiple irs_hpd
pending */
+ dp_del_event(dp, EV_IRQ_HPD_INT);
+
ret = dp_display_usbpd_attention_cb(&dp->pdev->dev);
if (ret == -ECONNRESET) { /* cable unplugged */
dp->core_initialized = false;
@@ -1300,6 +1303,9 @@ static int dp_pm_suspend(struct device *dev)
/* host_init will be called at pm_resume */
dp->core_initialized = false;
+ /* system suspended, delete pending irq_hdps */
+ dp_del_event(dp, EV_IRQ_HPD_INT);
What happens if I suspend my device and when this function is running
I
toggle my monitor to use the HDMI input that is connected instead of
some
other input, maybe the second HDMI input? Wouldn't that generate an
HPD
interrupt to grab the attention of this device?
no,
At this time display is off. this mean dp controller is off and
mainlink has teared down.
it will start with plug in interrupt to bring dp controller up and
start link training.
irq_hpd can be generated only panel is at run time of operation mode
and need attention from host.
If host is shutting down, then no need to service pending irq_hpd.
+
mutex_unlock(&dp->event_mutex);
return 0;
@@ -1496,6 +1502,9 @@ int msm_dp_display_disable(struct msm_dp *dp,
struct drm_encoder *encoder)
/* stop sentinel checking */
dp_del_event(dp_display, EV_DISCONNECT_PENDING_TIMEOUT);
+ /* link is down, delete pending irq_hdps */
+ dp_del_event(dp_display, EV_IRQ_HPD_INT);
+
I'm becoming convinced that the whole kthread design and event queue
is
broken. These sorts of patches are working around the larger problem
that the kthread is running independently of the driver and irqs can
come in at any time but the event queue is not checked from the irq
handler to debounce the irq event. Is the event queue necessary at
all?
I wonder if it would be simpler to just use an irq thread and process
the hpd signal from there. Then we're guaranteed to not get an irq
again
until the irq thread is done processing the event. This would
naturally
debounce the irq hpd event that way.
event q just like bottom half of irq handler. it turns irq into event
and handle them sequentially.
irq_hpd is asynchronous event from panel to bring up attention of hsot
during run time of operation.
Here, the dongle is unplugged and main link had teared down so that no
need to service pending irq_hpd if any.
As Kuogee mentioned, IRQ_HPD is a message received from the panel and is
not like your typical HW generated IRQ. There is no guarantee that we
will not receive an IRQ_HPD until we are finished with processing of an
earlier HPD message or an IRQ_HPD message. For example - when you run
the protocol compliance, when we get a HPD from the sink, we are
expected to start reading DPCD, EDID and proceed with link training. As
soon as link training is finished (which is marked by a specific DPCD
register write), the sink is going to issue an IRQ_HPD. At this point,
we may not done with processing the HPD high as after link training we
would typically notify the user mode of the newly connected display,
etc.
dp_display_disable(dp_display, 0);
rc = dp_display_unprepare(dp);
