linux-kernel - Re: [PATCH] drm: xlnx: zynqmp_dpsub: also call drm_helper_hpd_irq

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Message-ID: <7ded426e8e18dc8ce571a0ba623719b7910f4eb4.camel@dirkwinkel.cc>
Date: Mon, 21 Oct 2024 15:19:30 +0200
From: Steffen Dirkwinkel <lists@...ffen.cc>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	dri-devel@...ts.freedesktop.org, Maarten Lankhorst	
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Michal Simek <michal.simek@....com>,
 linux-arm-kernel@...ts.infradead.org, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: xlnx: zynqmp_dpsub: also call
 drm_helper_hpd_irq_event

On Sat, 2024-10-19 at 18:11 +0300, Dmitry Baryshkov wrote:
> On Wed, Oct 09, 2024 at 04:28:26PM +0200, Steffen Dirkwinkel wrote:
> > Hi Laurent,
> > 
> > 
> > On Wed, 2024-09-25 at 19:36 +0300, Laurent Pinchart wrote:
> > > Hi Steffen,
> > > 
> > > On Wed, Sep 25, 2024 at 09:54:18AM +0200, Steffen Dirkwinkel
> > > wrote:
> > > > On Tue, 2024-09-24 at 21:43 +0300, Laurent Pinchart wrote:
> > > > > On Mon, Sep 23, 2024 at 09:48:03AM +0200,
> > > > > lists@...ffen.cc wrote:
> > > > > > From: Steffen Dirkwinkel <s.dirkwinkel@...khoff.com>
> > > > > > 
> > > > > > With hpd going through the bridge as of commit eb2d64bfcc17
> > > > > > ("drm: xlnx: zynqmp_dpsub: Report HPD through the bridge")
> > > > > > we don't get hotplug events in userspace on zynqmp
> > > > > > hardware.
> > > > > > Also sending hotplug events with drm_helper_hpd_irq_event
> > > > > > works.
> > > > > 
> > > > > Why does the driver need to call both
> > > > > drm_helper_hpd_irq_event()
> > > > > and
> > > > > drm_bridge_hpd_notify() ? The latter should end up calling
> > > > > drm_kms_helper_connector_hotplug_event(), which is the same
> > > > > function
> > > > > that drm_helper_hpd_irq_event() calls.
> > > > 
> > > > I don't know why we need drm_helper_hpd_irq_event.
> > > > I'll try to trace what happens on hotplug.
> > > 
> > > Thank you. Let's try to find the best solution based on your
> > > findings.
> > 
> > There's just nothing registering for hpd with
> > "drm_bridge_connector_enable_hpd" or "drm_bridge_hpd_enable". I'm
> > not
> > sure what the correct way to implement this is. In
> > "drivers/gpu/drm/bridge/ti-tfp410.c" the driver registers for the
> > callback and calls "drm_helper_hpd_irq_event" in the callback. I
> > guess
> > we could also do that, but then we might as well call
> > drm_helper_hpd_irq_event directly? Some other drivers just call
> > both
> > like I did here. (drivers/gpu/drm/mediatek/mtk_hdmi.c for example)
> > For "drivers/gpu/drm/msm/hdmi/hdmi_bridge.c" I also can't find the
> > hpd
> > enable call and it just calls drm_bridge_hpd_notify.
> 
> The drm_bridge_connector handles enabling it for you when the driver
> calls drm_kms_helper_poll_init() / drm_kms_helper_poll_enable(). It
> seems zynqmp_kms calls drm_kms_helper_poll_init() too early, before
> creating DP chain, so the HPD doesn't get enabled.
Yes, that's it. Thank you

I'll send a patch for it.


> 
> > 
> > > 
> > > > > > Fixes: eb2d64bfcc17 ("drm: xlnx: zynqmp_dpsub: Report HPD
> > > > > > through
> > > > > > the bridge")
> > > > > > Signed-off-by: Steffen Dirkwinkel
> > > > > > <s.dirkwinkel@...khoff.com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
> > > > > >  1 file changed, 4 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > > > > b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > > > > index 1846c4971fd8..cb823540a412 100644
> > > > > > --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > > > > +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > > > > @@ -17,6 +17,7 @@
> > > > > >  #include <drm/drm_fourcc.h>
> > > > > >  #include <drm/drm_modes.h>
> > > > > >  #include <drm/drm_of.h>
> > > > > > +#include <drm/drm_probe_helper.h>
> > > > > >  
> > > > > >  #include <linux/clk.h>
> > > > > >  #include <linux/delay.h>
> > > > > > @@ -1614,6 +1615,9 @@ static void
> > > > > > zynqmp_dp_hpd_work_func(struct
> > > > > > work_struct *work)
> > > > > >  					   
> > > > > > hpd_work.work);
> > > > > >  	enum drm_connector_status status;
> > > > > >  
> > > > > > +	if (dp->bridge.dev)
> > > > > > +		drm_helper_hpd_irq_event(dp->bridge.dev);
> > > > > > +
> > > > > >  	status = zynqmp_dp_bridge_detect(&dp->bridge);
> > > > > >  	drm_bridge_hpd_notify(&dp->bridge, status);
> > > > > >  }
> > > 
> > 
>