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

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Message-ID: <yc43bbhfcc6nnrgxke2khkgcxxpt7mne2vmrggpkkc7gdwet4e@prpfb2wpgs66>
Date: Sat, 19 Oct 2024 18:11:51 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Steffen Dirkwinkel <lists@...ffen.cc>
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 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.

> 
> > 
> > > > > 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);
> > > > >  }
> > 
> 

-- 
With best wishes
Dmitry