[Intel-gfx] [PATCH 2/3] drm/i915: Introduce dual_bsd_ring parameter.

[Xiang, Haihao]

On Mon, 2014-06-30 at 09:51 -0700, Rodrigo Vivi wrote:
> On Broadwell GT3 we have 2 Video Command Streamers (VCS),
> but userspace has no control when using VCS1 or VCS2. So we cannot test,
> validate or debug specific changes or workaround that might affect only
> one or another ring. So this patch introduces a mechanism to avoid the
> ping-pong selection and use one specific ring given at boot time.

Hi, rodrigo

Could you use a mechanism to specify the ring at runtime ? If so, it is
flexible for us to use VCS ?

Thanks
Haihao

> 
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h            |  1 +
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 34 ++++++++++++++++++------------
>  drivers/gpu/drm/i915/i915_params.c         |  6 ++++++
>  3 files changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 8cea596..7b6614f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2069,6 +2069,7 @@ struct i915_params {
>  	int panel_ignore_lid;
>  	unsigned int powersave;
>  	int semaphores;
> +	int dual_bsd_ring;
>  	unsigned int lvds_downclock;
>  	int lvds_channel_mode;
>  	int panel_use_ssc;
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index d815ef5..09f350e 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1035,26 +1035,32 @@ static int gen8_dispatch_bsd_ring(struct drm_device *dev,
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_i915_file_private *file_priv = file->driver_priv;
> +	int ring_id;
> +	int dual = i915.dual_bsd_ring;
>  
>  	/* Check whether the file_priv is using one ring */
>  	if (file_priv->bsd_ring)
>  		return file_priv->bsd_ring->id;
> -	else {
> -		/* If no, use the ping-pong mechanism to select one ring */
> -		int ring_id;
>  
> -		mutex_lock(&dev->struct_mutex);
> -		if (dev_priv->mm.bsd_ring_dispatch_index == 0) {
> -			ring_id = VCS;
> -			dev_priv->mm.bsd_ring_dispatch_index = 1;
> -		} else {
> -			ring_id = VCS2;
> -			dev_priv->mm.bsd_ring_dispatch_index = 0;
> -		}
> -		file_priv->bsd_ring = &dev_priv->ring[ring_id];
> -		mutex_unlock(&dev->struct_mutex);
> -		return ring_id;
> +	/* If no, use the parameter defined or ping-pong mechanism
> +	 * to select one ring */
> +	mutex_lock(&dev->struct_mutex);
> +
> +	if (dual == 1 || (dual != 2 &&
> +			  dev_priv->mm.bsd_ring_dispatch_index == 0)) {
> +		ring_id = VCS;
> +		dev_priv->mm.bsd_ring_dispatch_index = 1;
> +	} else {
> +		ring_id = VCS2;
> +		dev_priv->mm.bsd_ring_dispatch_index = 0;
>  	}
> +
> +	file_priv->bsd_ring = &dev_priv->ring[ring_id];
> +	mutex_unlock(&dev->struct_mutex);
> +
> +	WARN(dual, "Forcibly trying to use only one bsd ring. Using: %s\n",
> +	     file_priv->bsd_ring->name);
> +	return ring_id;
>  }
>  
>  static struct drm_i915_gem_object *
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 8145729..d4871c8 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -29,6 +29,7 @@ struct i915_params i915 __read_mostly = {
>  	.panel_ignore_lid = 1,
>  	.powersave = 1,
>  	.semaphores = -1,
> +	.dual_bsd_ring = 0,
>  	.lvds_downclock = 0,
>  	.lvds_channel_mode = 0,
>  	.panel_use_ssc = -1,
> @@ -70,6 +71,11 @@ MODULE_PARM_DESC(semaphores,
>  	"Use semaphores for inter-ring sync "
>  	"(default: -1 (use per-chip defaults))");
>  
> +module_param_named(dual_bsd_ring, i915.dual_bsd_ring, int, 0600);
> +MODULE_PARM_DESC(dual_bsd_ring,
> +	 "Specify bds rings for VCS when there are multiple VCSs available."
> +	 "(0=All available bsd rings [default], 1=only VCS1, 2=only VCS2)");
> +
>  module_param_named(enable_rc6, i915.enable_rc6, int, 0400);
>  MODULE_PARM_DESC(enable_rc6,
>  	"Enable power-saving render C-state 6. "