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

Ander Conselvan De Oliveira
2016-05-06T13:07:47Z

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 *