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

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Message-ID: <20250808095259.GA31443@grimfrac.localdomain>
Date: Fri, 8 Aug 2025 11:52:59 +0200
From: Henrik Grimler <henrik@...mler.se>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
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

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.

> What is the order of events in such a case?

Order of events as in function tracing log? I enabled function tracing
with these filters:

  'max77693_muic_*' 'samsung_dsim_*' 'drm_bridge_*'
  'drm_atomic_bridge_*' 'exynos_irq_*' 'hdmi*' 'sii9234_*'

and captured the calls when I connect cable. dmesg with debug output
at the same time gives:

[ 6568.462521] max77693-muic max77693-muic: external connector is attached (adc:0x00, prev_adc:0x0)
[ 6568.470575] max77693-charger max77693-charger: not charging. connector type: 13
[ 6568.491722] sii9234 15-0039: sii9234: detection started d3
[ 6569.398148] i2c i2c-15: sendbytes: NAK bailout.
[ 6569.401477] sii9234 15-0039: writebm:  TPI[0x3d] <- 0x3e
[ 6569.408403] max77693-muic max77693-muic: external connector is attached (adc:0x00, prev_adc:0x0)
[ 6569.422638] max77693-charger max77693-charger: not charging. connector type: 13
[ 6569.570615] sii9234 15-0039: sii9234_irq_thread
[ 6569.622846] sii9234 15-0039: irq 00/00 42/5c 00/00
[ 6569.626182] sii9234 15-0039: RGND_READY_INT
[ 6570.592367] sii9234 15-0039: sii9234_irq_thread
[ 6570.644626] sii9234 15-0039: irq 00/60 40/5c 00/00
[ 6570.656185] sii9234 15-0039: RGND 1K!!
[ 6570.937165] sii9234 15-0039: sii9234_irq_thread
[ 6570.989467] sii9234 15-0039: irq 20/60 00/5c 00/0c
[ 6571.000986] sii9234 15-0039: MHL cable connected.. RSEN High
[ 6571.222655] sii9234 15-0039: sii9234_irq_thread
[ 6571.274884] sii9234 15-0039: irq 00/60 04/5c 00/04
[ 6571.278219] sii9234 15-0039: mhl est interrupt
[ 6571.408117] sii9234 15-0039: sii9234_irq_thread
[ 6571.460346] sii9234 15-0039: irq 40/60 00/5c 00/04

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.

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
>