Re: [PATCHv4 1/3] drm/i915: Make finding unused crtc as a generic function

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Mon, 2016-04-18 at 19:01 +0530, Durgadoss R wrote:
> Looping over the crtc list and finding an unused crtc
> has other users like upfront link training. Hence move it to

"will have", since this patch precedes the upfront link training one.

> a common function to re-use the logic.
> 
> v4:
> * Added ERR_PTR as a return value in kernel Doc comment (Ander)
> v3:
> * Added kernel Doc and removed an invalid comment (Ander)
> * Rebased on top of latest code which includes locking
>   for state->enable usage.
> v2:
> * Made this as a separate function instead of having it
>   inside upfront link train code.
> 
> Signed-off-by: Durgadoss R <durgadoss.r@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 74 +++++++++++++++++++++------------
> ---
>  drivers/gpu/drm/i915/intel_drv.h     |  2 +
>  2 files changed, 45 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c
> b/drivers/gpu/drm/i915/intel_display.c
> index 4cca155..a6df48b 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10404,6 +10404,43 @@ static int intel_modeset_setup_plane_state(struct
> drm_atomic_state *state,
>  	return 0;
>  }
>  
> +/**
> + * intel_get_unused_crtc - Find an unused crtc for the given encoder
> + * @encoder: drm_encoder structure
> + * @ctx: ctx pointer to use with locking
> + *
> + * This function tries to find an unused crtc that can drive
> + * the given encoder. Returns NULL or ERR_PTR on failure.

This NULL or ERR_PTR makes for an awkward interface. I wonder if it should just
return ERR_PTR(-EBUSY) or even ERR_PTR(-EINVAL) if there is no free crtc. It's
no big deal though.

Also, in the success case crtc->mutex is kept locked. That should be added to
the documentation above.

> + */
> +struct drm_crtc *intel_get_unused_crtc(struct drm_encoder *encoder,
> +				struct drm_modeset_acquire_ctx *ctx)
> +{
> +	struct drm_crtc *possible_crtc;
> +	struct drm_crtc *crtc = NULL;
> +	struct drm_device *dev = encoder->dev;
> +	int ret, i = -1;
> +
> +	for_each_crtc(dev, possible_crtc) {
> +		i++;
> +		if (!(encoder->possible_crtcs & (1 << i)))
> +			continue;
> +
> +		ret = drm_modeset_lock(&possible_crtc->mutex, ctx);
> +		if (ret)
> +			return ERR_PTR(ret);
> +
> +		if (possible_crtc->state->enable) {
> +			drm_modeset_unlock(&possible_crtc->mutex);
> +			continue;
> +		}
> +
> +		crtc = possible_crtc;
> +		break;

This could be replaced with "return possible_crtc;". No need for the extra
assignment and break.

I see that in patch 3 you have a debug message for when this returns NULL. It
would make sense to move that debug here.

Ander

> +	}
> +
> +	return crtc;
> +}
> +
>  bool intel_get_load_detect_pipe(struct drm_connector *connector,
>  				struct drm_display_mode *mode,
>  				struct intel_load_detect_pipe *old,
> @@ -10412,7 +10449,6 @@ bool intel_get_load_detect_pipe(struct drm_connector
> *connector,
>  	struct intel_crtc *intel_crtc;
>  	struct intel_encoder *intel_encoder =
>  		intel_attached_encoder(connector);
> -	struct drm_crtc *possible_crtc;
>  	struct drm_encoder *encoder = &intel_encoder->base;
>  	struct drm_crtc *crtc = NULL;
>  	struct drm_device *dev = encoder->dev;
> @@ -10421,7 +10457,7 @@ bool intel_get_load_detect_pipe(struct drm_connector
> *connector,
>  	struct drm_atomic_state *state = NULL, *restore_state = NULL;
>  	struct drm_connector_state *connector_state;
>  	struct intel_crtc_state *crtc_state;
> -	int ret, i = -1;
> +	int ret;
>  
>  	DRM_DEBUG_KMS("[CONNECTOR:%d:%s], [ENCODER:%d:%s]\n",
>  		      connector->base.id, connector->name,
> @@ -10451,39 +10487,15 @@ retry:
>  		ret = drm_modeset_lock(&crtc->mutex, ctx);
>  		if (ret)
>  			goto fail;
> -
> -		/* Make sure the crtc and connector are running */
> -		goto found;
> -	}
> -
> -	/* Find an unused one (if possible) */
> -	for_each_crtc(dev, possible_crtc) {
> -		i++;
> -		if (!(encoder->possible_crtcs & (1 << i)))
> -			continue;
> -
> -		ret = drm_modeset_lock(&possible_crtc->mutex, ctx);
> -		if (ret)
> +	} else {
> +		crtc = intel_get_unused_crtc(encoder, ctx);
> +		if (IS_ERR_OR_NULL(crtc)) {
> +			ret = PTR_ERR_OR_ZERO(crtc);
> +			DRM_DEBUG_KMS("no pipe available for load-detect\n");
>  			goto fail;
> -
> -		if (possible_crtc->state->enable) {
> -			drm_modeset_unlock(&possible_crtc->mutex);
> -			continue;
>  		}
> -
> -		crtc = possible_crtc;
> -		break;
> -	}
> -
> -	/*
> -	 * If we didn't find an unused CRTC, don't use any.
> -	 */
> -	if (!crtc) {
> -		DRM_DEBUG_KMS("no pipe available for load-detect\n");
> -		goto fail;
>  	}
>  
> -found:
>  	intel_crtc = to_intel_crtc(crtc);
>  
>  	ret = drm_modeset_lock(&crtc->primary->mutex, ctx);
> diff --git a/drivers/gpu/drm/i915/intel_drv.h
> b/drivers/gpu/drm/i915/intel_drv.h
> index e13ce22..27b5dcd 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1159,6 +1159,8 @@ bool intel_get_load_detect_pipe(struct drm_connector
> *connector,
>  void intel_release_load_detect_pipe(struct drm_connector *connector,
>  				    struct intel_load_detect_pipe *old,
>  				    struct drm_modeset_acquire_ctx *ctx);
> +struct drm_crtc *intel_get_unused_crtc(struct drm_encoder *encoder,
> +				struct drm_modeset_acquire_ctx *ctx);
>  int intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
>  			       unsigned int rotation);
>  struct drm_framebuffer *
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