linux-kernel - Re: [PATCH v2 3/3] drm/bridge: sii9234: use extcon cable detection logic to detect MHL

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Message-ID: <r2u2odrkzfezohq44nh4jw6oj23j46gohuzsh6k7jpwnzojxqk@vdus4jj5lv7x>
Date: Mon, 18 Aug 2025 03:42:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Henrik Grimler <henrik@...mler.se>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-samsung-soc@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, replicant@...osl.org,
        linux-kernel@...r.kernel.org, m.szyprowski@...sung.com
Subject: Re: [PATCH v2 3/3] drm/bridge: sii9234: use extcon cable detection
 logic to detect MHL

On Fri, Aug 08, 2025 at 11:52:59AM +0200, Henrik Grimler wrote:
> Hi Dmitry,
> 
> On Sun, Jul 27, 2025 at 08:07:37PM +0300, Dmitry Baryshkov wrote:
> > On Thu, Jul 24, 2025 at 08:50:53PM +0200, Henrik Grimler wrote:
> > > To use MHL we currently need the MHL chip to be permanently on, which
> > > consumes unnecessary power. Let's use extcon attached to MUIC to enable
> > > the MHL chip only if it detects an MHL cable.
> > 
> > Does HPD GPIO reflect the correct state of the cable?
> 
> Yes, the HPD gpio pin changes state from low to high when a mhl cable is
> connected:
> 
> $ sudo cat /sys/kernel/debug/gpio|grep gpio-755
>  gpio-755 (                    |hpd                 ) in  lo IRQ
> $ sudo cat /sys/kernel/debug/gpio|grep gpio-755
>  gpio-755 (                    |hpd                 ) in  hi IRQ
> 
> so that is described correctly.
> 

Ack.

> 
> and in captured trace I see that on cable connect we get an irq that
> is handled through:
> 1. max77693_muic_irq_handler
> 2. max77693_muic_irq_work
> 3. max77693_muic_adc_handler
> 4. sii9234_extcon_notifier
> 5. sii9234_extcon_work
> 6. sii9234_cable_in
> 7. hdmi_irq_thread
> 
> Raw captured trace dat file can be found here:
> https://grimler.se/files/sii9234-mhl-connect-trace.dat
> 
> Maybe you were asking for some other type of order of events log
> though, please let me know if I misunderstand.
> 
> > Should the sii9234 signal to Exynos HDMI that the link is established?
> 
> Maybe.. Sorry, I do not know enough about extcon and drm yet. I assume
> you mean through drm_helper_hpd_irq_event() and
> drm_bridge_hpd_notify(), I will experiment a bit and add it to the
> driver and see if this improves it.

If you are getting the HDMI IRQ event, then I'd suggest checking that
you are actually getting the 'plugged' event, etc. I was worried that
you are hijacking the DRM chain. But if you are getting hotplug events,
then it's fine (and most likely correct).

> 
> There is currently (as I wrote to Marek Szyprowski in a response in
> v1) an issue where device screen stops working if cable is connected
> when device screen is off, maybe proper notification would help..
> 
> > > Signed-off-by: Henrik Grimler <henrik@...mler.se>
> > > ---
> > > v2: add dependency on extcon. Issue reported by kernel test robot
> > >     <lkp@...el.com>
> > > ---
> > >  drivers/gpu/drm/bridge/Kconfig   |  1 +
> > >  drivers/gpu/drm/bridge/sii9234.c | 89 ++++++++++++++++++++++++++++++++++++++--
> > >  2 files changed, 87 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > > index b9e0ca85226a603a24f90c6879d1499f824060cb..f18a083f6e1c6fe40bde5e65a1548acc61a162ae 100644
> > > --- a/drivers/gpu/drm/bridge/Kconfig
> > > +++ b/drivers/gpu/drm/bridge/Kconfig
> > > @@ -303,6 +303,7 @@ config DRM_SII902X
> > >  config DRM_SII9234
> > >  	tristate "Silicon Image SII9234 HDMI/MHL bridge"
> > >  	depends on OF
> > > +	select EXTCON
> > 
> > Either this or 'depends on EXTCON || !EXTCON'
> 
> Feels like depends is a better description so will change to it,
> thanks!
> 
> Best regards,
> Henrik Grimler
> 
> > >  	help
> > >  	  Say Y here if you want support for the MHL interface.
> > >  	  It is an I2C driver, that detects connection of MHL bridge
> > 
> > -- 
> > With best wishes
> > Dmitry
> > 

-- 
With best wishes
Dmitry