linux-kernel - Re: [PATCH] drm/i2c: tda998x: Fix lockdep warning about possible circular dependency

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Message-ID: <20170720130829.GY31807@n2100.armlinux.org.uk>
Date:   Thu, 20 Jul 2017 14:08:29 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Liviu Dudau <Liviu.Dudau@....com>
Cc:     David Airlie <airlied@...ux.ie>,
        DRI devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/i2c: tda998x: Fix lockdep warning about possible
 circular dependency

On Thu, Jul 20, 2017 at 01:54:04PM +0100, Liviu Dudau wrote:
> On Thu, Jul 20, 2017 at 12:44:49PM +0100, Russell King - ARM Linux wrote:
> > Actually, scrub that idea - drm_helper_probe_single_connector_modes()
> > calls drm_edid_to_eld() for these cases anyway, so we must call
> > drm_helper_probe_single_connector_modes() with the audio_mutex held.
> 
> OK, so the lockdep warning is spurious?

I don't think so.  I think there's two ways to solve this:

1. replace the audio_mutex in tda998x_audio_get_eld() and
   tda998x_connector_fill_modes() with a new mutex (eld_mutex) to
   protect just the ELD.

2. remove the mutex from these two functions, and take the connection_mutex
   modeset lock in tda998x_audio_get_eld().

However, I don't have a view on which would be best.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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