[PATCH v3 05/33] drm: Pass the drm_dp_aux->hw_mutex to i2c for its locking

[Ville Syrjälä]

On Fri, Jun 03, 2016 at 03:36:48PM +0100, Chris Wilson wrote:
> Rather than have both drm_dp_aux lock within its transfer, and i2c to
> lock around the transfer, use the same lock by filling in the locking
> callbacks that i2c wants to use. We require our own hw_mutex as we
> bypass i2c_transfer for drm_dp_dpcd_access().
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Rafael Antognolli <rafael.antognolli at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: dri-devel at lists.freedesktop.org
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index eeaf5a7c3aa7..4b088afa21b2 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -708,8 +708,6 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  
>  	memset(&msg, 0, sizeof(msg));
>  
> -	mutex_lock(&aux->hw_mutex);
> -
>  	for (i = 0; i < num; i++) {
>  		msg.address = msgs[i].addr;
>  		drm_dp_i2c_msg_set_request(&msg, &msgs[i]);
> @@ -764,8 +762,6 @@ static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
>  	msg.size = 0;
>  	(void)drm_dp_i2c_do_msg(aux, &msg);
>  
> -	mutex_unlock(&aux->hw_mutex);
> -
>  	return err;
>  }

AFAICS the only functional difference will be that we'll hold the lock
across the retries performed by the core. Looks like we set the retry
count to 3 for whatever reason, but I'm not seeing that we'd ever
actually return -EAGAIN so I guess the core will neever retry.
Oh, actually if we ever end up in the trylock path
(in_atomic||irqs_disabled) then the core would retry. But I don't think
we should ever do that.

Patch seems OK to me:
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

>  
> @@ -774,6 +770,26 @@ static const struct i2c_algorithm drm_dp_i2c_algo = {
>  	.master_xfer = drm_dp_i2c_xfer,
>  };
>  
> +static struct drm_dp_aux *i2c_to_aux(struct i2c_adapter *i2c)
> +{
> +	return container_of(i2c, struct drm_dp_aux, ddc);
> +}
> +
> +static void lock_bus(struct i2c_adapter *i2c, unsigned int flags)
> +{
> +	mutex_lock(&i2c_to_aux(i2c)->hw_mutex);
> +}
> +
> +static int trylock_bus(struct i2c_adapter *i2c, unsigned int flags)
> +{
> +	return mutex_trylock(&i2c_to_aux(i2c)->hw_mutex);
> +}
> +
> +static void unlock_bus(struct i2c_adapter *i2c, unsigned int flags)
> +{
> +	mutex_unlock(&i2c_to_aux(i2c)->hw_mutex);
> +}
> +
>  /**
>   * drm_dp_aux_register() - initialise and register aux channel
>   * @aux: DisplayPort AUX channel
> @@ -790,6 +806,10 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
>  	aux->ddc.algo_data = aux;
>  	aux->ddc.retries = 3;
>  
> +	aux->ddc.lock_bus = lock_bus;
> +	aux->ddc.trylock_bus = trylock_bus;
> +	aux->ddc.unlock_bus = unlock_bus;
> +
>  	aux->ddc.class = I2C_CLASS_DDC;
>  	aux->ddc.owner = THIS_MODULE;
>  	aux->ddc.dev.parent = aux->dev;
> -- 
> 2.8.1

-- 
Ville Syrjälä
Intel OTC