Re: [PATCH v3 06/33] drm: Minimally initialise drm_dp_aux

Re: [PATCH v3 06/33] drm: Minimally initialise drm_dp_aux

[Ville Syrjälä]

On Fri, Jun 03, 2016 at 03:36:49PM +0100, Chris Wilson wrote:
> When trying to split up the initialisation phase and the registration
> phase, one immediate problem encountered is trying to use our own i2c
> devices before registration with userspace (to read EDID during device
> discovery). drm_dp_aux in particular only offers an interface for setting
> up the device *after* we have exposed the connector via sysfs. In order
> to break the chicken-and-egg problem, export drm_dp_aux_init() to
> minimally prepare the i2c device for internal use before
> drm_connector_register().
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Rafael Antognolli <rafael.antognolli@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: dri-devel@lists.freedesktop.org
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 26 +++++++++++++++++++++-----
>  include/drm/drm_dp_helper.h     |  1 +
>  2 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 4b088afa21b2..9b4ec65e1de6 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -791,15 +791,16 @@ static void unlock_bus(struct i2c_adapter *i2c, unsigned int flags)
>  }
>  
>  /**
> - * drm_dp_aux_register() - initialise and register aux channel
> + * drm_dp_aux_init() - minimally initialise an aux channel
>   * @aux: DisplayPort AUX channel
>   *
> - * Returns 0 on success or a negative error code on failure.
> + * If you need to use the drm_dp_aux's i2c adapter prior to registering it
> + * with the outside world, call drm_dp_aux_init() first. You must still
> + * call drm_dp_aux_register() once the connector has been registered to
> + * allow userspace access to the auxiliary DP channel.
>   */
> -int drm_dp_aux_register(struct drm_dp_aux *aux)
> +void drm_dp_aux_init(struct drm_dp_aux *aux)
>  {
> -	int ret;
> -
>  	mutex_init(&aux->hw_mutex);
>  
>  	aux->ddc.algo = &drm_dp_i2c_algo;
> @@ -809,6 +810,21 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
>  	aux->ddc.lock_bus = lock_bus;
>  	aux->ddc.trylock_bus = trylock_bus;
>  	aux->ddc.unlock_bus = unlock_bus;
> +}
> +EXPORT_SYMBOL(drm_dp_aux_init);

This doesn't feel very safe to me. To me it looks like the i2c core
wasn't designed to have the adapter be used before i2c_add_adapter()
is called. I guess it might work in this case since you provide your
own lock vfuncs.

I think someone should fix the i2c core to split i2c_add_adapter()
& co. into init and register phases. Cc:ing i2c folks...

> +
> +/**
> + * drm_dp_aux_register() - initialise and register aux channel
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_register(struct drm_dp_aux *aux)
> +{
> +	int ret;
> +
> +	if (!aux->ddc.algo)
> +		drm_dp_aux_init(aux);
>  
>  	aux->ddc.class = I2C_CLASS_DDC;
>  	aux->ddc.owner = THIS_MODULE;
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 5a848e734422..4d85cf2874af 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -805,6 +805,7 @@ int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
>  
> +void drm_dp_aux_init(struct drm_dp_aux *aux);
>  int drm_dp_aux_register(struct drm_dp_aux *aux);
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux);
>  
> -- 
> 2.8.1

-- 
Ville Syrjälä
Intel OTC
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Re: [PATCH v3 06/33] drm: Minimally initialise drm_dp_aux

[Chris Wilson]

On Fri, Jun 03, 2016 at 05:59:11PM +0300, Ville Syrjälä wrote:
> On Fri, Jun 03, 2016 at 03:36:49PM +0100, Chris Wilson wrote:
> > When trying to split up the initialisation phase and the registration
> > phase, one immediate problem encountered is trying to use our own i2c
> > devices before registration with userspace (to read EDID during device
> > discovery). drm_dp_aux in particular only offers an interface for setting
> > up the device *after* we have exposed the connector via sysfs. In order
> > to break the chicken-and-egg problem, export drm_dp_aux_init() to
> > minimally prepare the i2c device for internal use before
> > drm_connector_register().
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Dave Airlie <airlied@redhat.com>
> > Cc: Rafael Antognolli <rafael.antognolli@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: dri-devel@lists.freedesktop.org
> > ---
> >  drivers/gpu/drm/drm_dp_helper.c | 26 +++++++++++++++++++++-----
> >  include/drm/drm_dp_helper.h     |  1 +
> >  2 files changed, 22 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > index 4b088afa21b2..9b4ec65e1de6 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -791,15 +791,16 @@ static void unlock_bus(struct i2c_adapter *i2c, unsigned int flags)
> >  }
> >  
> >  /**
> > - * drm_dp_aux_register() - initialise and register aux channel
> > + * drm_dp_aux_init() - minimally initialise an aux channel
> >   * @aux: DisplayPort AUX channel
> >   *
> > - * Returns 0 on success or a negative error code on failure.
> > + * If you need to use the drm_dp_aux's i2c adapter prior to registering it
> > + * with the outside world, call drm_dp_aux_init() first. You must still
> > + * call drm_dp_aux_register() once the connector has been registered to
> > + * allow userspace access to the auxiliary DP channel.
> >   */
> > -int drm_dp_aux_register(struct drm_dp_aux *aux)
> > +void drm_dp_aux_init(struct drm_dp_aux *aux)
> >  {
> > -	int ret;
> > -
> >  	mutex_init(&aux->hw_mutex);
> >  
> >  	aux->ddc.algo = &drm_dp_i2c_algo;
> > @@ -809,6 +810,21 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
> >  	aux->ddc.lock_bus = lock_bus;
> >  	aux->ddc.trylock_bus = trylock_bus;
> >  	aux->ddc.unlock_bus = unlock_bus;
> > +}
> > +EXPORT_SYMBOL(drm_dp_aux_init);
> 
> This doesn't feel very safe to me. To me it looks like the i2c core
> wasn't designed to have the adapter be used before i2c_add_adapter()
> is called. I guess it might work in this case since you provide your
> own lock vfuncs.
> 
> I think someone should fix the i2c core to split i2c_add_adapter()
> & co. into init and register phases. Cc:ing i2c folks...

As you've seen, I sent the patches to split i2c_add_adapter() to allow for
us to call i2c_init_adapter() here instead. It still requires the same
basic review that this init (the same as above) is sufficient for using
i2c_transfer().

I would like to get the regression fix completed without much futher
ado - in particular, not depending upon landing an external patch.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

Re: [PATCH v3 06/33] drm: Minimally initialise drm_dp_aux

[Ville Syrjälä]

On Thu, Jun 09, 2016 at 09:57:24PM +0100, Chris Wilson wrote:
> On Fri, Jun 03, 2016 at 05:59:11PM +0300, Ville Syrjälä wrote:
> > On Fri, Jun 03, 2016 at 03:36:49PM +0100, Chris Wilson wrote:
> > > When trying to split up the initialisation phase and the registration
> > > phase, one immediate problem encountered is trying to use our own i2c
> > > devices before registration with userspace (to read EDID during device
> > > discovery). drm_dp_aux in particular only offers an interface for setting
> > > up the device *after* we have exposed the connector via sysfs. In order
> > > to break the chicken-and-egg problem, export drm_dp_aux_init() to
> > > minimally prepare the i2c device for internal use before
> > > drm_connector_register().
> > > 
> > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Dave Airlie <airlied@redhat.com>
> > > Cc: Rafael Antognolli <rafael.antognolli@intel.com>
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Cc: dri-devel@lists.freedesktop.org
> > > ---
> > >  drivers/gpu/drm/drm_dp_helper.c | 26 +++++++++++++++++++++-----
> > >  include/drm/drm_dp_helper.h     |  1 +
> > >  2 files changed, 22 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > > index 4b088afa21b2..9b4ec65e1de6 100644
> > > --- a/drivers/gpu/drm/drm_dp_helper.c
> > > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > > @@ -791,15 +791,16 @@ static void unlock_bus(struct i2c_adapter *i2c, unsigned int flags)
> > >  }
> > >  
> > >  /**
> > > - * drm_dp_aux_register() - initialise and register aux channel
> > > + * drm_dp_aux_init() - minimally initialise an aux channel
> > >   * @aux: DisplayPort AUX channel
> > >   *
> > > - * Returns 0 on success or a negative error code on failure.
> > > + * If you need to use the drm_dp_aux's i2c adapter prior to registering it
> > > + * with the outside world, call drm_dp_aux_init() first. You must still
> > > + * call drm_dp_aux_register() once the connector has been registered to
> > > + * allow userspace access to the auxiliary DP channel.
> > >   */
> > > -int drm_dp_aux_register(struct drm_dp_aux *aux)
> > > +void drm_dp_aux_init(struct drm_dp_aux *aux)
> > >  {
> > > -	int ret;
> > > -
> > >  	mutex_init(&aux->hw_mutex);
> > >  
> > >  	aux->ddc.algo = &drm_dp_i2c_algo;
> > > @@ -809,6 +810,21 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
> > >  	aux->ddc.lock_bus = lock_bus;
> > >  	aux->ddc.trylock_bus = trylock_bus;
> > >  	aux->ddc.unlock_bus = unlock_bus;
> > > +}
> > > +EXPORT_SYMBOL(drm_dp_aux_init);
> > 
> > This doesn't feel very safe to me. To me it looks like the i2c core
> > wasn't designed to have the adapter be used before i2c_add_adapter()
> > is called. I guess it might work in this case since you provide your
> > own lock vfuncs.
> > 
> > I think someone should fix the i2c core to split i2c_add_adapter()
> > & co. into init and register phases. Cc:ing i2c folks...
> 
> As you've seen, I sent the patches to split i2c_add_adapter() to allow for
> us to call i2c_init_adapter() here instead. It still requires the same
> basic review that this init (the same as above) is sufficient for using
> i2c_transfer().
> 
> I would like to get the regression fix completed without much futher
> ado - in particular, not depending upon landing an external patch.

What regression is this?

-- 
Ville Syrjälä
Intel OTC

Re: [PATCH v3 06/33] drm: Minimally initialise drm_dp_aux

[Chris Wilson]

On Fri, Jun 10, 2016 at 01:26:24PM +0300, Ville Syrjälä wrote:
> On Thu, Jun 09, 2016 at 09:57:24PM +0100, Chris Wilson wrote:
> > On Fri, Jun 03, 2016 at 05:59:11PM +0300, Ville Syrjälä wrote:
> > > On Fri, Jun 03, 2016 at 03:36:49PM +0100, Chris Wilson wrote:
> > > > When trying to split up the initialisation phase and the registration
> > > > phase, one immediate problem encountered is trying to use our own i2c
> > > > devices before registration with userspace (to read EDID during device
> > > > discovery). drm_dp_aux in particular only offers an interface for setting
> > > > up the device *after* we have exposed the connector via sysfs. In order
> > > > to break the chicken-and-egg problem, export drm_dp_aux_init() to
> > > > minimally prepare the i2c device for internal use before
> > > > drm_connector_register().
> > > > 
> > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Cc: Dave Airlie <airlied@redhat.com>
> > > > Cc: Rafael Antognolli <rafael.antognolli@intel.com>
> > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > Cc: dri-devel@lists.freedesktop.org
> > > > ---
> > > >  drivers/gpu/drm/drm_dp_helper.c | 26 +++++++++++++++++++++-----
> > > >  include/drm/drm_dp_helper.h     |  1 +
> > > >  2 files changed, 22 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> > > > index 4b088afa21b2..9b4ec65e1de6 100644
> > > > --- a/drivers/gpu/drm/drm_dp_helper.c
> > > > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > > > @@ -791,15 +791,16 @@ static void unlock_bus(struct i2c_adapter *i2c, unsigned int flags)
> > > >  }
> > > >  
> > > >  /**
> > > > - * drm_dp_aux_register() - initialise and register aux channel
> > > > + * drm_dp_aux_init() - minimally initialise an aux channel
> > > >   * @aux: DisplayPort AUX channel
> > > >   *
> > > > - * Returns 0 on success or a negative error code on failure.
> > > > + * If you need to use the drm_dp_aux's i2c adapter prior to registering it
> > > > + * with the outside world, call drm_dp_aux_init() first. You must still
> > > > + * call drm_dp_aux_register() once the connector has been registered to
> > > > + * allow userspace access to the auxiliary DP channel.
> > > >   */
> > > > -int drm_dp_aux_register(struct drm_dp_aux *aux)
> > > > +void drm_dp_aux_init(struct drm_dp_aux *aux)
> > > >  {
> > > > -	int ret;
> > > > -
> > > >  	mutex_init(&aux->hw_mutex);
> > > >  
> > > >  	aux->ddc.algo = &drm_dp_i2c_algo;
> > > > @@ -809,6 +810,21 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
> > > >  	aux->ddc.lock_bus = lock_bus;
> > > >  	aux->ddc.trylock_bus = trylock_bus;
> > > >  	aux->ddc.unlock_bus = unlock_bus;
> > > > +}
> > > > +EXPORT_SYMBOL(drm_dp_aux_init);
> > > 
> > > This doesn't feel very safe to me. To me it looks like the i2c core
> > > wasn't designed to have the adapter be used before i2c_add_adapter()
> > > is called. I guess it might work in this case since you provide your
> > > own lock vfuncs.
> > > 
> > > I think someone should fix the i2c core to split i2c_add_adapter()
> > > & co. into init and register phases. Cc:ing i2c folks...
> > 
> > As you've seen, I sent the patches to split i2c_add_adapter() to allow for
> > us to call i2c_init_adapter() here instead. It still requires the same
> > basic review that this init (the same as above) is sufficient for using
> > i2c_transfer().
> > 
> > I would like to get the regression fix completed without much futher
> > ado - in particular, not depending upon landing an external patch.
> 
> What regression is this?

It all started from the unclaimed mmio access across suspend, which
stems from never having touched a context before suspend. That in turn
meant touching the delayed rps initialisation which ended up with Daniel
saying that the entire init chain needs to be unravelled. Snowball.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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