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Message-ID: <20250818142622.GA286180@grimfrac.localdomain>
Date: Mon, 18 Aug 2025 16:26:22 +0200
From: Henrik Grimler <henrik@...mler.se>
To: Marek Szyprowski <m.szyprowski@...sung.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
Subject: Re: [PATCH v2 3/3] drm/bridge: sii9234: use extcon cable detection
 logic to detect MHL

Hi Marek,

On Thu, Aug 14, 2025 at 01:26:33PM +0200, Marek Szyprowski wrote:
> On 24.07.2025 20:50, 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.
> >
> > 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
> >   	help
> >   	  Say Y here if you want support for the MHL interface.
> >   	  It is an I2C driver, that detects connection of MHL bridge
> > diff --git a/drivers/gpu/drm/bridge/sii9234.c b/drivers/gpu/drm/bridge/sii9234.c
> > index 0e0bb1bf71fdcef788715cfd6fa158a6992def33..4d84ba01ea76816bebdbc29d48a041c9c6cd508e 100644
> > --- a/drivers/gpu/drm/bridge/sii9234.c
> > +++ b/drivers/gpu/drm/bridge/sii9234.c

[ ...]

> > +
> > +	edev = extcon_find_edev_by_node(muic);
> > +	of_node_put(muic);
> > +	if (IS_ERR(edev)) {
> > +		dev_err_probe(ctx->dev, PTR_ERR(edev),
> > +			      "invalid or missing extcon\n");
> > +	}
> 
> It looks that the original logic got lost somehow in the above code 
> block, what causes kernel oops if compiled as module and loaded before 
> extcon provider. Please handle -EPROBE_DEFER and propagate error value, 
> like the original code did in sii8620 driver:
> 
>          if (IS_ERR(edev)) {
>                  if (PTR_ERR(edev) == -EPROBE_DEFER)
>                          return -EPROBE_DEFER;
>                  dev_err(ctx->dev, "Invalid or missing extcon\n");
>                  return PTR_ERR(edev);
>          }

Thanks for detecting the issue! I think my code is just missing return
before dev_err_probe (same mistake as I did on patch 2). With return
added I have not been able to reproduce any kernel oops, but if
CONFIG_DRM_SII9234=y and CONFIG_EXTCON_MAX77693=m then it seems like
linux gets stuck probing sii9234 and waiting for the extcon provider
(verified with some printf debugging). This happens for me both with:

	edev = extcon_find_edev_by_node(muic);
	of_node_put(muic);
	if (IS_ERR(edev)) {
		return dev_err_probe(ctx->dev, PTR_ERR(edev),
				     "Invalid or missing extcon\n");
	}

and

	edev = extcon_find_edev_by_node(muic);
	of_node_put(muic);
	if (IS_ERR(edev)) {
		if (PTR_ERR(edev) == -EPROBE_DEFER)
			return -EPROBE_DEFER;
		dev_err(ctx->dev, "Invalid or missing extcon\n");
		return PTR_ERR(edev);
	}

I am not sure what to do to fix the issue, as far as I can see probe
logic and extcon handling is the same as in sil-sii8620 and ite-it6505
(i.e. the other bridges that use extcon). Will investigate further.

Best regards,
Henrik Grimler

> > +
> > +	ctx->extcon = edev;
> > +	ctx->extcon_nb.notifier_call = sii9234_extcon_notifier;
> > +	INIT_WORK(&ctx->extcon_wq, sii9234_extcon_work);
> > +	ret = extcon_register_notifier(edev, EXTCON_DISP_MHL, &ctx->extcon_nb);
> > +	if (ret) {
> > +		dev_err(ctx->dev, "failed to register notifier for MHL\n");
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >   static enum drm_mode_status sii9234_mode_valid(struct drm_bridge *bridge,
> >   					 const struct drm_display_info *info,
> >   					 const struct drm_display_mode *mode)
> > @@ -916,12 +986,17 @@ static int sii9234_probe(struct i2c_client *client)
> >   	if (ret < 0)
> >   		return ret;
> >   
> > +	ret = sii9234_extcon_init(ctx);
> > +	if (ret < 0)
> > +		return ret;
> > +
> >   	i2c_set_clientdata(client, ctx);
> >   
> >   	ctx->bridge.of_node = dev->of_node;
> >   	drm_bridge_add(&ctx->bridge);
> >   
> > -	sii9234_cable_in(ctx);
> > +	if (!ctx->extcon)
> > +		sii9234_cable_in(ctx);
> >   
> >   	return 0;
> >   }
> > @@ -930,7 +1005,15 @@ static void sii9234_remove(struct i2c_client *client)
> >   {
> >   	struct sii9234 *ctx = i2c_get_clientdata(client);
> >   
> > -	sii9234_cable_out(ctx);
> > +	if (ctx->extcon) {
> > +		extcon_unregister_notifier(ctx->extcon, EXTCON_DISP_MHL,
> > +					   &ctx->extcon_nb);
> > +		flush_work(&ctx->extcon_wq);
> > +		if (ctx->cable_state > 0)
> > +			sii9234_cable_out(ctx);
> > +	} else {
> > +		sii9234_cable_out(ctx);
> > +	}
> >   	drm_bridge_remove(&ctx->bridge);
> >   }
> >   
> >
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 

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