[PATCH] drm/i915: Fix enc_to_dig_port() for MST encoders

[Jani Nikula]

On Wed, 27 Apr 2016, Lyude <cpaul at redhat.com> wrote:
> For MST encoders, the encoder struct is stored in the intel_dp_mst
> struct, not a intel_digital_port struct.
>
> This fixes issues with hotplugging MST displays that support MST audio,
> where hotplugging had a surprisingly good chance of accidentally
> overwriting other parts of the kernel leading to seemingly unrelated
> backtraces in sysfs, ext4, etc.
>
> Cc: stable at vger.kernel.org
> Signed-off-by: Lyude <cpaul at redhat.com>

Ugh. Just ugh.

At a glance, it's probably this one that starts calling
intel_audio_codec_enable() and intel_audio_codec_disable() on DP MST:

commit 3d52ccf52f2c51f613e42e65be0f06e4e6788093
Author: Libin Yang <libin.yang at linux.intel.com>
Date:   Wed Dec 2 14:09:44 2015 +0800

    drm/i915: start adding dp mst audio

which has been there since v4.5. Would it be feasible for you to revert
the commit or change it so that it stops calling the audio codec
enable/disable, to verify this is the culprit? So we could add a proper
Fixes: line too.

The non-MST aware enc_to_dig_port() calls on platforms that might have
MST were added in:

commit 51e1d83cab9988716ae68801a721f4df0aaa374b
Author: David Henningsson <david.henningsson at canonical.com>
Date:   Wed Aug 19 10:48:56 2015 +0200

    drm/i915: Call audio pin/ELD notify function

and:

commit 7e8275c2f2bbb384e18af37066b8b2f32b7d092f
Author: Libin Yang <libin.yang at intel.com>
Date:   Fri Sep 25 09:36:12 2015 +0800

    drm/i915: set proper N/CTS in modeset

but I don't think the codec enable/disable were called on MST at that
time.

Some of the problem was probably seen by Takashi in

commit 0bdf5a05647a66dcc6394986e061daeac9b1cf96
Author: Takashi Iwai <tiwai at suse.de>
Date:   Mon Nov 30 18:19:39 2015 +0100

    drm/i915: Add reverse mapping between port and intel_encoder

which has a comment /* intel_encoder might be NULL for DP MST */. Maybe
that needs to be updated to DTRT too.


Lyude, thanks for your efforts in DP MST area. Much appreciated.


BR,
Jani.



> ---
>  drivers/gpu/drm/i915/intel_drv.h | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 4c027d6..81f2212 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -918,18 +918,23 @@ intel_attached_encoder(struct drm_connector *connector)
>  	return to_intel_connector(connector)->encoder;
>  }
>  
> -static inline struct intel_digital_port *
> -enc_to_dig_port(struct drm_encoder *encoder)
> -{
> -	return container_of(encoder, struct intel_digital_port, base.base);
> -}
> -
>  static inline struct intel_dp_mst_encoder *
>  enc_to_mst(struct drm_encoder *encoder)
>  {
>  	return container_of(encoder, struct intel_dp_mst_encoder, base.base);
>  }
>  
> +static inline struct intel_digital_port *
> +enc_to_dig_port(struct drm_encoder *encoder)
> +{
> +	if (encoder->encoder_type == DRM_MODE_ENCODER_DPMST)
> +		return enc_to_mst(encoder)->primary;
> +	else {
> +		return container_of(encoder, struct intel_digital_port,
> +				    base.base);
> +	}
> +}
> +
>  static inline struct intel_dp *enc_to_intel_dp(struct drm_encoder *encoder)
>  {
>  	return &enc_to_dig_port(encoder)->dp;

-- 
Jani Nikula, Intel Open Source Technology Center