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

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Message-ID: <20240925163609.GD27666@pendragon.ideasonboard.com>
Date: Wed, 25 Sep 2024 19:36:09 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Steffen Dirkwinkel <lists@...ffen.cc>
Cc: 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

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.

> > > 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);
> > >  }

-- 
Regards,

Laurent Pinchart