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

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Message-ID: <20250824111129.GA37114@grimfrac.localdomain>
Date: Sun, 24 Aug 2025 13:11:29 +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 Mon, Aug 18, 2025 at 03:42:07AM +0300, Dmitry Baryshkov wrote:
> 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).

With some debugging in sii9234_extcon_notifier added:

--- a/drivers/gpu/drm/bridge/sii9234.c
+++ b/drivers/gpu/drm/bridge/sii9234.c
@@ -892,6 +892,8 @@ static int sii9234_extcon_notifier(struct notifier_block *self,
        struct sii9234 *ctx =
                container_of(self, struct sii9234, extcon_nb);
 
+       dev_info(ctx->dev, "extcon event %lu\n", event);
+
        schedule_work(&ctx->extcon_wq);
 
        return NOTIFY_DONE;

I see that sii9234 receives the hotplug event. On plug in:

[  532.132981] sii9234 15-0039: extcon event 0
[  532.136601] max77693-muic max77693-muic: external connector is attached (adc:0x00, prev_adc:0x0)
[  532.142777] sii9234 15-0039: RSEN_HIGH without RGND_1K
[  532.149815] sii9234 15-0039: extcon event 1
[  532.155662] max77693-charger max77693-charger: not charging. connector type: 13
[  532.164801] sii9234 15-0039: extcon event 0
[  532.168371] max77693-muic max77693-muic: external connector is detached(chg_type:0x0, prev_chg_type:0x0)
[  532.178370] sii9234 15-0039: extcon event 0
[  532.188250] max77693-charger max77693-charger: not charging. connector type: 13
[  533.097415] i2c i2c-15: sendbytes: NAK bailout.
[  533.100735] sii9234 15-0039: writebm:  TPI[0x3d] <- 0x3e
[  533.115161] sii9234 15-0039: writeb:  TPI[0x3d] <- 0x00

and disconnect:

[  547.195219] dwc2 12480000.usb: new device is full-speed
[  547.204912] max77693-muic max77693-muic: external connector is attached (adc:0x00, prev_adc:0x0)
[  547.212629] sii9234 15-0039: extcon event 1
[  547.218304] max77693-charger max77693-charger: not charging. connector type: 13
[  548.159257] i2c i2c-15: sendbytes: NAK bailout.
[  548.162602] sii9234 15-0039: writebm:  TPI[0x3d] <- 0x3e
[  548.167990] sii9234 15-0039: extcon event 0
[  548.172788] max77693-muic max77693-muic: external connector is attached (adc:0x00, prev_adc:0x0)
[  548.181336] sii9234 15-0039: extcon event 1
[  548.186510] max77693-charger max77693-charger: not charging. connector type: 13

It seems a bit weird to me that it receives multiple events, but maybe
that is expected. Will send a v3 shortly, thank you!

Best regards,
Henrik Grimler