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

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Message-ID: <6cea659387e14f0436105053416a42c4729923b3.camel@dirkwinkel.cc>
Date: Wed, 09 Oct 2024 16:28:26 +0200
From: Steffen Dirkwinkel <lists@...ffen.cc>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
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 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.

> 
> > > > 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);
> > > >  }
>