Re: [PATCH] drm: refcnt drm_framebuffer

On Tue, Sep 04, 2012 at 06:10:04PM -0500, Rob Clark wrote:

From: Rob Clark rob@ti.com

This simplifies drm fb lifetime, and if the crtc/plane needs to hold a ref to the fb when disabling a pipe until the next vblank, this avoids the need to make disabling an overlay synchronous. This is a problem that shows up when userspace is using a drm plane to implement a hw cursor.. making overlay disable synchronous causes a performance problem when x11 is rapidly enabling/disabling the hw cursor. But not making it synchronous opens up a race condition for crashing if userspace turns around and immediately deletes the fb. Refcnt'ing the fb makes it possible to solve this problem.

v1: original v2: add drm_framebuffer_remove() which is called in all paths where fb->funcs->destroy() was directly called before. This cleans up the CRTCs/planes that the fb was attached to. You should only directly use drm_framebuffer_unreference() if you are also using drm_framebuffer_reference() to keep a ref to the fb.

Signed-off-by: Rob Clark rob@ti.com

Yeah, this could also be rather useful to move a few things to saner places in drm/i915. The fb->refcount is a bit strange though since only driver-internals can be reference counted, all the userspace interface stuff in the drm core has to abide to the old api which mandates that we remove all uses of a given fb at rmfb time. I guess we'll just have to live with that.

Still, can you add a small comment in drm_crtc.h to the new refcount explaining this? And maybe extend the note about the ->destroy callback to say "call _remove or _unrefence instead"? Otherwise

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

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drivers/gpu/drm/drm_crtc.c | 78 +++++++++++++++++++++++++---- drivers/gpu/drm/exynos/exynos_drm_fbdev.c | 4 +- drivers/gpu/drm/i915/intel_display.c | 4 +- drivers/staging/omapdrm/omap_fbdev.c | 4 +- include/drm/drm_crtc.h | 5 ++ 5 files changed, 78 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index 901de9a..96e236f 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -294,6 +294,8 @@ int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb, { int ret;

• kref_init(&fb->refcount);
• ret = drm_mode_object_get(dev, &fb->base, DRM_MODE_OBJECT_FB); if (ret) return ret;

@@ -307,6 +309,38 @@ int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb, } EXPORT_SYMBOL(drm_framebuffer_init);

+static void drm_framebuffer_free(struct kref *kref) +{

• struct drm_framebuffer *fb =

• 	container_of(kref, struct drm_framebuffer, refcount);
  

• fb->funcs->destroy(fb);

+}

+/**

• • drm_framebuffer_unreference - unref a framebuffer
• • LOCKING:
• • Caller must hold mode config lock.
• */

+void drm_framebuffer_unreference(struct drm_framebuffer *fb) +{

• struct drm_device *dev = fb->dev;
• DRM_DEBUG("FB ID: %d\n", fb->base.id);
• WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
• kref_put(&fb->refcount, drm_framebuffer_free);

+} +EXPORT_SYMBOL(drm_framebuffer_unreference);

+/**

• • drm_framebuffer_reference - incr the fb refcnt
• */

+void drm_framebuffer_reference(struct drm_framebuffer *fb) +{

• DRM_DEBUG("FB ID: %d\n", fb->base.id);
• kref_get(&fb->refcount);

+} +EXPORT_SYMBOL(drm_framebuffer_reference);

/**

• drm_framebuffer_cleanup - remove a framebuffer object
• @fb: framebuffer to remove

@@ -320,6 +354,32 @@ EXPORT_SYMBOL(drm_framebuffer_init); void drm_framebuffer_cleanup(struct drm_framebuffer *fb) { struct drm_device *dev = fb->dev;

• /*

• * This could be moved to drm_framebuffer_remove(), but for
  

• * debugging is nice to keep around the list of fb's that are
  

• * no longer associated w/ a drm_file but are not unreferenced
  

• * yet.  (i915 and omapdrm have debugfs files which will show
  

• * this.)
  

• */
  

• drm_mode_object_put(dev, &fb->base);
• list_del(&fb->head);
• dev->mode_config.num_fb--;

+} +EXPORT_SYMBOL(drm_framebuffer_cleanup);

+/**

• • drm_framebuffer_remove - remove and unreference a framebuffer object
• • @fb: framebuffer to remove
• • LOCKING:
• • Caller must hold mode config lock.
• • Scans all the CRTCs and planes in @dev's mode_config. If they're
• • using @fb, removes it, setting it to NULL.
• */

+void drm_framebuffer_remove(struct drm_framebuffer *fb) +{

• struct drm_device *dev = fb->dev; struct drm_crtc *crtc; struct drm_plane *plane; struct drm_mode_set set;

@@ -350,11 +410,11 @@ void drm_framebuffer_cleanup(struct drm_framebuffer *fb) } }

• drm_mode_object_put(dev, &fb->base);
• list_del(&fb->head);
• dev->mode_config.num_fb--;

• list_del(&fb->filp_head);
• drm_framebuffer_unreference(fb);

} -EXPORT_SYMBOL(drm_framebuffer_cleanup); +EXPORT_SYMBOL(drm_framebuffer_remove);

/**

• drm_crtc_init - Initialise a new CRTC object

@@ -1032,7 +1092,7 @@ void drm_mode_config_cleanup(struct drm_device *dev) }

list_for_each_entry_safe(fb, fbt, &dev->mode_config.fb_list, head) {

• fb->funcs->destroy(fb);
  

• drm_framebuffer_remove(fb);
  

  }

  list_for_each_entry_safe(crtc, ct, &dev->mode_config.crtc_list, head) {

@@ -2343,11 +2403,8 @@ int drm_mode_rmfb(struct drm_device *dev, goto out; }

• /* TODO release all crtc connected to the framebuffer */
• /* TODO unhock the destructor from the buffer object */
• list_del(&fb->filp_head);
• fb->funcs->destroy(fb);

• drm_framebuffer_remove(fb);

out: mutex_unlock(&dev->mode_config.mutex); @@ -2497,8 +2554,7 @@ void drm_fb_release(struct drm_file *priv)

mutex_lock(&dev->mode_config.mutex); list_for_each_entry_safe(fb, tfb, &priv->fbs, filp_head) {

• list_del(&fb->filp_head);
  

• fb->funcs->destroy(fb);
  

• drm_framebuffer_remove(fb);
  

  } mutex_unlock(&dev->mode_config.mutex);

} diff --git a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c index d5586cc..f4ac433 100644 --- a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c +++ b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c @@ -266,8 +266,8 @@ static void exynos_drm_fbdev_destroy(struct drm_device *dev, /* release drm framebuffer and real buffer */ if (fb_helper->fb && fb_helper->fb->funcs) { fb = fb_helper->fb;

• if (fb && fb->funcs->destroy)
  

• 	fb->funcs->destroy(fb);
  

• if (fb)
  

• 	drm_framebuffer_remove(fb);
  

  }

  /* release linux framebuffer */

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index a69a3d0..2109c9f 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -5687,7 +5687,7 @@ bool intel_get_load_detect_pipe(struct intel_encoder *intel_encoder, if (!drm_crtc_helper_set_mode(crtc, mode, 0, 0, old_fb)) { DRM_DEBUG_KMS("failed to set mode on load-detect pipe\n"); if (old->release_fb)

• 	old->release_fb->funcs->destroy(old->release_fb);
  

• 	drm_framebuffer_remove(old->release_fb);
  

  crtc->fb = old_fb; return false; }

@@ -5717,7 +5717,7 @@ void intel_release_load_detect_pipe(struct intel_encoder *intel_encoder, drm_helper_disable_unused_functions(dev);

if (old->release_fb)

• 	old->release_fb->funcs->destroy(old->release_fb);
  

• 	drm_framebuffer_remove(old->release_fb);
  
  

  return; }

diff --git a/drivers/staging/omapdrm/omap_fbdev.c b/drivers/staging/omapdrm/omap_fbdev.c index 8c6ed3b..8a027bb 100644 --- a/drivers/staging/omapdrm/omap_fbdev.c +++ b/drivers/staging/omapdrm/omap_fbdev.c @@ -276,7 +276,7 @@ fail: if (fbi) framebuffer_release(fbi); if (fb)

• 	fb->funcs->destroy(fb);
  

• 	drm_framebuffer_remove(fb);
  

  }

  return ret;

@@ -401,7 +401,7 @@ void omap_fbdev_free(struct drm_device *dev)

/* this will free the backing object */ if (fbdev->fb)

• fbdev->fb->funcs->destroy(fbdev->fb);
  

• drm_framebuffer_remove(fbdev->fb);
  
  

  kfree(fbdev);

diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index a82e0a2..2442d01 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -219,6 +219,7 @@ struct drm_display_info { };

struct drm_framebuffer_funcs {

• /* note: use drm_framebuffer_remove() */ void (*destroy)(struct drm_framebuffer *framebuffer); int (*create_handle)(struct drm_framebuffer *fb, struct drm_file *file_priv,

@@ -243,6 +244,7 @@ struct drm_framebuffer_funcs {

struct drm_framebuffer { struct drm_device *dev;

• struct kref refcount; struct list_head head; struct drm_mode_object base; const struct drm_framebuffer_funcs *funcs;

@@ -921,6 +923,9 @@ extern int drm_object_property_get_value(struct drm_mode_object *obj, extern int drm_framebuffer_init(struct drm_device *dev, struct drm_framebuffer *fb, const struct drm_framebuffer_funcs *funcs); +void drm_framebuffer_unreference(struct drm_framebuffer *fb); +void drm_framebuffer_reference(struct drm_framebuffer *fb); +void drm_framebuffer_remove(struct drm_framebuffer *fb); extern void drm_framebuffer_cleanup(struct drm_framebuffer *fb);

extern void drm_connector_attach_property(struct drm_connector *connector,

1.7.9.5

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