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

R, Durgadoss
2016-05-09T09:45:52Z

> -----Original Message-----
> From: Ander Conselvan De Oliveira [mailto:conselvan2@gmail.com]
> Sent: Friday, May 6, 2016 6:38 PM
> To: R, Durgadoss <durgadoss.r@intel.com>; intel-gfx@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCHv4 1/3] drm/i915: Make finding unused crtc as
> a generic function
>
> 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.
>

Ok, Will make the failure case as return (-EINVAL).

> > + */
> > +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.

Sure, will add it here..

Thanks,
Durga

>
> 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 *