drm/i915: Pin the ifbdev for the info->system_base GGTT mmapping

Commit Message

Wayne Boyer Oct. 8, 2015, 8:50 p.m. UTC

From: Chris Wilson <[e-mail]>

A long time ago (before 3.14) we relied on a permanent pinning of the
ifbdev to lock the fb in place inside the GGTT. However, the
introduction of stealing the BIOS framebuffer and reusing its address in
the GGTT for the fbdev has muddied waters and we use an inherited fb.
However, the inherited fb is only pinned whilst it is active and we no
longer have an explicit pin for the info->system_base mmapping used by
the fbdev. The result is that after some aperture pressure the fbdev may
be evicted, but we continue to write the fbcon into the same GGTT
address - overwriting anything else that may be put into that offset.
The effect is most pronounced across suspend/resume as
intel_fbdev_set_suspend() does a full clear over the whole scanout.

v2: rebased on latest nightly (Wayne)
v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
on Chris' review. (Wayne)

Signed-off-by: Chris Wilson <[e-mail]>
Cc: "Goel, Akash" <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Jesse Barnes <[e-mail]>
Cc: [e-mail]
Reviewed-by: Deepak S <[e-mail]>
Signed-off-by: Wayne Boyer <[e-mail]>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

Comments

Chris Wilson Oct. 9, 2015, 9:11 a.m. UTC | #1

On Thu, Oct 08, 2015 at 01:50:21PM -0700, Wayne Boyer wrote:
> From: Chris Wilson <[e-mail]>
> 
> A long time ago (before 3.14) we relied on a permanent pinning of the
> ifbdev to lock the fb in place inside the GGTT. However, the
> introduction of stealing the BIOS framebuffer and reusing its address in
> the GGTT for the fbdev has muddied waters and we use an inherited fb.
> However, the inherited fb is only pinned whilst it is active and we no
> longer have an explicit pin for the info->system_base mmapping used by
> the fbdev. The result is that after some aperture pressure the fbdev may
> be evicted, but we continue to write the fbcon into the same GGTT
> address - overwriting anything else that may be put into that offset.
> The effect is most pronounced across suspend/resume as
> intel_fbdev_set_suspend() does a full clear over the whole scanout.
> 
> v2: rebased on latest nightly (Wayne)
> v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> on Chris' review. (Wayne)

Note that this patch also depends on the

	drm/i915: Set the map-and-fenceable flag for preallocated objects

fix as well
http://patchwork.freedesktop.org/patch/58026/
-Chris

Jani Nikula Oct. 9, 2015, noon UTC | #2

On Fri, 09 Oct 2015, Chris Wilson <[e-mail]> wrote:
> On Thu, Oct 08, 2015 at 01:50:21PM -0700, Wayne Boyer wrote:
>> From: Chris Wilson <[e-mail]>
>> 
>> A long time ago (before 3.14) we relied on a permanent pinning of the
>> ifbdev to lock the fb in place inside the GGTT. However, the
>> introduction of stealing the BIOS framebuffer and reusing its address in
>> the GGTT for the fbdev has muddied waters and we use an inherited fb.
>> However, the inherited fb is only pinned whilst it is active and we no
>> longer have an explicit pin for the info->system_base mmapping used by
>> the fbdev. The result is that after some aperture pressure the fbdev may
>> be evicted, but we continue to write the fbcon into the same GGTT
>> address - overwriting anything else that may be put into that offset.
>> The effect is most pronounced across suspend/resume as
>> intel_fbdev_set_suspend() does a full clear over the whole scanout.
>> 
>> v2: rebased on latest nightly (Wayne)
>> v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
>> on Chris' review. (Wayne)
>
> Note that this patch also depends on the
>
> 	drm/i915: Set the map-and-fenceable flag for preallocated objects
>
> fix as well
> http://patchwork.freedesktop.org/patch/58026/

Jesse, please provide your Tested-by on that plus this patch, since you
reported the breakage [1] that got the two patches reverted in the first
place.

Thanks,
Jani.


[1] http://mid.gmane.org/[e-mail]

> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre
> _______________________________________________
> Intel-gfx mailing list
> [e-mail]
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Dave Gordon Oct. 23, 2015, 9:17 p.m. UTC | #3

On 08/10/15 21:50, Wayne Boyer wrote:
> From: Chris Wilson <[e-mail]>
>
> A long time ago (before 3.14) we relied on a permanent pinning of the
> ifbdev to lock the fb in place inside the GGTT. However, the
> introduction of stealing the BIOS framebuffer and reusing its address in
> the GGTT for the fbdev has muddied waters and we use an inherited fb.
> However, the inherited fb is only pinned whilst it is active and we no
> longer have an explicit pin for the info->system_base mmapping used by
> the fbdev. The result is that after some aperture pressure the fbdev may
> be evicted, but we continue to write the fbcon into the same GGTT
> address - overwriting anything else that may be put into that offset.
> The effect is most pronounced across suspend/resume as
> intel_fbdev_set_suspend() does a full clear over the whole scanout.
>
> v2: rebased on latest nightly (Wayne)
> v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> on Chris' review. (Wayne)
>
> Signed-off-by: Chris Wilson <[e-mail]>
> Cc: "Goel, Akash" <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Cc: Jesse Barnes <[e-mail]>
> Cc: [e-mail]
> Reviewed-by: Deepak S <[e-mail]>
> Signed-off-by: Wayne Boyer <[e-mail]>
> ---
>   drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6532912..0ad46521 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
>   	obj = intel_fb->obj;
>   	size = obj->base.size;
>
> +	/* The fb constructor will have already pinned us (or inherited a
> +	 * GGTT region from the BIOS) suitable for a scanout, so
> +	 * this should just be a no-op and increment the pin count for the
> +	 * fbdev mmapping. It does have a useful side-effect of validating
> +	 * the pin for fbdev's use via a GGTT mmapping.
> +	 */
> +	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> +	if (ret)
> +		goto out_unlock;
> +
>   	info = drm_fb_helper_alloc_fbi(helper);
>   	if (IS_ERR(info)) {
>   		ret = PTR_ERR(info);
> @@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
>   out_destroy_fbi:
>   	drm_fb_helper_release_fbi(helper);
>   out_unpin:
> +	/* Once for info->screen_base mmaping... */
> +	i915_gem_object_ggtt_unpin(obj);
> +	/* ...and once for the intel_fb */
>   	i915_gem_object_ggtt_unpin(obj);
>   	drm_gem_object_unreference(&obj->base);
>   out_unlock:
> @@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
>   static void intel_fbdev_destroy(struct drm_device *dev,
>   				struct intel_fbdev *ifbdev)
>   {
> +	/* Release the pinning for the info->screen_base mmaping. */
> +	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
>
>   	drm_fb_helper_unregister_fbi(&ifbdev->helper);
>   	drm_fb_helper_release_fbi(&ifbdev->helper);

Hmm .. pinning now done by i915_gem_obj_ggtt_pin(), but the unpinning 
function is i915_gem_object_ggtt_unpin(). Just the sort of asymmetry 
that helps everyone understand what's going on :(

Could we not have a mass rename of the various i915_gem_obj{ect} 
functions to ONE consistent naming convention? (Personally I prefer 
'obj' because it's shorter, but consistency is more important than 
saving just 3 letters).

.Dave.

Lukas Wunner Oct. 25, 2015, 2:34 p.m. UTC | #4

Hi,

On Thu, Oct 08, 2015 at 01:50:21PM -0700, Wayne Boyer wrote:
> From: Chris Wilson <[e-mail]>
> 
> A long time ago (before 3.14) we relied on a permanent pinning of the
> ifbdev to lock the fb in place inside the GGTT. However, the
> introduction of stealing the BIOS framebuffer and reusing its address in
> the GGTT for the fbdev has muddied waters and we use an inherited fb.
> However, the inherited fb is only pinned whilst it is active and we no
> longer have an explicit pin for the info->system_base mmapping used by
> the fbdev. The result is that after some aperture pressure the fbdev may
> be evicted, but we continue to write the fbcon into the same GGTT
> address - overwriting anything else that may be put into that offset.
> The effect is most pronounced across suspend/resume as
> intel_fbdev_set_suspend() does a full clear over the whole scanout.
> 
> v2: rebased on latest nightly (Wayne)
> v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> on Chris' review. (Wayne)
> 
> Signed-off-by: Chris Wilson <[e-mail]>
> Cc: "Goel, Akash" <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Cc: Jesse Barnes <[e-mail]>
> Cc: [e-mail]
> Reviewed-by: Deepak S <[e-mail]>
> Signed-off-by: Wayne Boyer <[e-mail]>
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6532912..0ad46521 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	/* The fb constructor will have already pinned us (or inherited a
> +	 * GGTT region from the BIOS) suitable for a scanout, so
> +	 * this should just be a no-op and increment the pin count for the
> +	 * fbdev mmapping. It does have a useful side-effect of validating
> +	 * the pin for fbdev's use via a GGTT mmapping.
> +	 */
> +	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> +	if (ret)
> +		goto out_unlock;

I think a DRM_ERROR() should be added here, otherwise if this check fails,
the user will never be notified thereof. It's not sufficient to just
return a negative int because this just gets passed up the call stack to
intel_fbdev_initial_config() which ignores it.

I'm adding DRM_ERROR() invocations to the two existing error conditions in
this function with patch 4 of the series I just posted to intel-gfx:

Link: http://lists.freedesktop.org/archives/intel-gfx/2015-October/078837.html
Message-Id: <[e-mail]>

Best regards,

Lukas


> +
>  	info = drm_fb_helper_alloc_fbi(helper);
>  	if (IS_ERR(info)) {
>  		ret = PTR_ERR(info);
> @@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_destroy_fbi:
>  	drm_fb_helper_release_fbi(helper);
>  out_unpin:
> +	/* Once for info->screen_base mmaping... */
> +	i915_gem_object_ggtt_unpin(obj);
> +	/* ...and once for the intel_fb */
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
>  out_unlock:
> @@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
>  static void intel_fbdev_destroy(struct drm_device *dev,
>  				struct intel_fbdev *ifbdev)
>  {
> +	/* Release the pinning for the info->screen_base mmaping. */
> +	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
>  
>  	drm_fb_helper_unregister_fbi(&ifbdev->helper);
>  	drm_fb_helper_release_fbi(&ifbdev->helper);
> -- 
> 1.9.1
> 
> _______________________________________________
> Intel-gfx mailing list
> [e-mail]
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Lukas Wunner Oct. 25, 2015, 2:53 p.m. UTC | #5

Another observation that occurred to me only after sending away my
previous message (sorry):

On Thu, Oct 08, 2015 at 01:50:21PM -0700, Wayne Boyer wrote:
> From: Chris Wilson <[e-mail]>
> 
> A long time ago (before 3.14) we relied on a permanent pinning of the
> ifbdev to lock the fb in place inside the GGTT. However, the
> introduction of stealing the BIOS framebuffer and reusing its address in
> the GGTT for the fbdev has muddied waters and we use an inherited fb.
> However, the inherited fb is only pinned whilst it is active and we no
> longer have an explicit pin for the info->system_base mmapping used by
> the fbdev. The result is that after some aperture pressure the fbdev may
> be evicted, but we continue to write the fbcon into the same GGTT
> address - overwriting anything else that may be put into that offset.
> The effect is most pronounced across suspend/resume as
> intel_fbdev_set_suspend() does a full clear over the whole scanout.

Since this only concerns the case when the fb was inherited from BIOS,
why don't you invoke i915_gem_obj_ggtt_pin() only in this particular case?
It's discernible from the prealloc variable.

I think then you also don't need to call i915_gem_object_ggtt_unpin() twice.


> 
> v2: rebased on latest nightly (Wayne)
> v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> on Chris' review. (Wayne)
> 
> Signed-off-by: Chris Wilson <[e-mail]>
> Cc: "Goel, Akash" <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Cc: Jesse Barnes <[e-mail]>
> Cc: [e-mail]
> Reviewed-by: Deepak S <[e-mail]>
> Signed-off-by: Wayne Boyer <[e-mail]>
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6532912..0ad46521 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	/* The fb constructor will have already pinned us (or inherited a
> +	 * GGTT region from the BIOS) suitable for a scanout, so
> +	 * this should just be a no-op and increment the pin count for the
> +	 * fbdev mmapping. It does have a useful side-effect of validating
> +	 * the pin for fbdev's use via a GGTT mmapping.
> +	 */
> +	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> +	if (ret)
> +		goto out_unlock;
> +
>  	info = drm_fb_helper_alloc_fbi(helper);
>  	if (IS_ERR(info)) {
>  		ret = PTR_ERR(info);
> @@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_destroy_fbi:
>  	drm_fb_helper_release_fbi(helper);
>  out_unpin:
> +	/* Once for info->screen_base mmaping... */
> +	i915_gem_object_ggtt_unpin(obj);
> +	/* ...and once for the intel_fb */
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
>  out_unlock:
> @@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
>  static void intel_fbdev_destroy(struct drm_device *dev,
>  				struct intel_fbdev *ifbdev)
>  {
> +	/* Release the pinning for the info->screen_base mmaping. */
> +	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
>  
>  	drm_fb_helper_unregister_fbi(&ifbdev->helper);
>  	drm_fb_helper_release_fbi(&ifbdev->helper);
> -- 
> 1.9.1
> 
> _______________________________________________
> Intel-gfx mailing list
> [e-mail]
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Daniel Vetter Oct. 30, 2015, 4:18 p.m. UTC | #6

On Fri, Oct 23, 2015 at 10:17:44PM +0100, Dave Gordon wrote:
> On 08/10/15 21:50, Wayne Boyer wrote:
> >From: Chris Wilson <[e-mail]>
> >
> >A long time ago (before 3.14) we relied on a permanent pinning of the
> >ifbdev to lock the fb in place inside the GGTT. However, the
> >introduction of stealing the BIOS framebuffer and reusing its address in
> >the GGTT for the fbdev has muddied waters and we use an inherited fb.
> >However, the inherited fb is only pinned whilst it is active and we no
> >longer have an explicit pin for the info->system_base mmapping used by
> >the fbdev. The result is that after some aperture pressure the fbdev may
> >be evicted, but we continue to write the fbcon into the same GGTT
> >address - overwriting anything else that may be put into that offset.
> >The effect is most pronounced across suspend/resume as
> >intel_fbdev_set_suspend() does a full clear over the whole scanout.
> >
> >v2: rebased on latest nightly (Wayne)
> >v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> >on Chris' review. (Wayne)
> >
> >Signed-off-by: Chris Wilson <[e-mail]>
> >Cc: "Goel, Akash" <[e-mail]>
> >Cc: Daniel Vetter <[e-mail]>
> >Cc: Jesse Barnes <[e-mail]>
> >Cc: [e-mail]
> >Reviewed-by: Deepak S <[e-mail]>
> >Signed-off-by: Wayne Boyer <[e-mail]>
> >---
> >  drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> >index 6532912..0ad46521 100644
> >--- a/drivers/gpu/drm/i915/intel_fbdev.c
> >+++ b/drivers/gpu/drm/i915/intel_fbdev.c
> >@@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
> >  	obj = intel_fb->obj;
> >  	size = obj->base.size;
> >
> >+	/* The fb constructor will have already pinned us (or inherited a
> >+	 * GGTT region from the BIOS) suitable for a scanout, so
> >+	 * this should just be a no-op and increment the pin count for the
> >+	 * fbdev mmapping. It does have a useful side-effect of validating
> >+	 * the pin for fbdev's use via a GGTT mmapping.
> >+	 */
> >+	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> >+	if (ret)
> >+		goto out_unlock;
> >+
> >  	info = drm_fb_helper_alloc_fbi(helper);
> >  	if (IS_ERR(info)) {
> >  		ret = PTR_ERR(info);
> >@@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
> >  out_destroy_fbi:
> >  	drm_fb_helper_release_fbi(helper);
> >  out_unpin:
> >+	/* Once for info->screen_base mmaping... */
> >+	i915_gem_object_ggtt_unpin(obj);
> >+	/* ...and once for the intel_fb */
> >  	i915_gem_object_ggtt_unpin(obj);
> >  	drm_gem_object_unreference(&obj->base);
> >  out_unlock:
> >@@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
> >  static void intel_fbdev_destroy(struct drm_device *dev,
> >  				struct intel_fbdev *ifbdev)
> >  {
> >+	/* Release the pinning for the info->screen_base mmaping. */
> >+	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
> >
> >  	drm_fb_helper_unregister_fbi(&ifbdev->helper);
> >  	drm_fb_helper_release_fbi(&ifbdev->helper);
> 
> Hmm .. pinning now done by i915_gem_obj_ggtt_pin(), but the unpinning
> function is i915_gem_object_ggtt_unpin(). Just the sort of asymmetry that
> helps everyone understand what's going on :(
> 
> Could we not have a mass rename of the various i915_gem_obj{ect} functions
> to ONE consistent naming convention? (Personally I prefer 'obj' because it's
> shorter, but consistency is more important than saving just 3 letters).

Of course, just needs someone to do it, and make sure to not step onto too
many toes. I'd love if more people actually take charge of gem instead of
piling more on top.
-Daniel

Chris Wilson Oct. 30, 2015, 5:17 p.m. UTC | #7

On Fri, Oct 30, 2015 at 05:18:15PM +0100, Daniel Vetter wrote:
> On Fri, Oct 23, 2015 at 10:17:44PM +0100, Dave Gordon wrote:
> > On 08/10/15 21:50, Wayne Boyer wrote:
> > >From: Chris Wilson <[e-mail]>
> > >
> > >A long time ago (before 3.14) we relied on a permanent pinning of the
> > >ifbdev to lock the fb in place inside the GGTT. However, the
> > >introduction of stealing the BIOS framebuffer and reusing its address in
> > >the GGTT for the fbdev has muddied waters and we use an inherited fb.
> > >However, the inherited fb is only pinned whilst it is active and we no
> > >longer have an explicit pin for the info->system_base mmapping used by
> > >the fbdev. The result is that after some aperture pressure the fbdev may
> > >be evicted, but we continue to write the fbcon into the same GGTT
> > >address - overwriting anything else that may be put into that offset.
> > >The effect is most pronounced across suspend/resume as
> > >intel_fbdev_set_suspend() does a full clear over the whole scanout.
> > >
> > >v2: rebased on latest nightly (Wayne)
> > >v3: changed i915_gem_object_ggtt_pin() to i915_gem_obj_ggtt_pin() based
> > >on Chris' review. (Wayne)
> > >
> > >Signed-off-by: Chris Wilson <[e-mail]>
> > >Cc: "Goel, Akash" <[e-mail]>
> > >Cc: Daniel Vetter <[e-mail]>
> > >Cc: Jesse Barnes <[e-mail]>
> > >Cc: [e-mail]
> > >Reviewed-by: Deepak S <[e-mail]>
> > >Signed-off-by: Wayne Boyer <[e-mail]>
> > >---
> > >  drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
> > >  1 file changed, 15 insertions(+)
> > >
> > >diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> > >index 6532912..0ad46521 100644
> > >--- a/drivers/gpu/drm/i915/intel_fbdev.c
> > >+++ b/drivers/gpu/drm/i915/intel_fbdev.c
> > >@@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper *helper,
> > >  	obj = intel_fb->obj;
> > >  	size = obj->base.size;
> > >
> > >+	/* The fb constructor will have already pinned us (or inherited a
> > >+	 * GGTT region from the BIOS) suitable for a scanout, so
> > >+	 * this should just be a no-op and increment the pin count for the
> > >+	 * fbdev mmapping. It does have a useful side-effect of validating
> > >+	 * the pin for fbdev's use via a GGTT mmapping.
> > >+	 */
> > >+	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> > >+	if (ret)
> > >+		goto out_unlock;
> > >+
> > >  	info = drm_fb_helper_alloc_fbi(helper);
> > >  	if (IS_ERR(info)) {
> > >  		ret = PTR_ERR(info);
> > >@@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
> > >  out_destroy_fbi:
> > >  	drm_fb_helper_release_fbi(helper);
> > >  out_unpin:
> > >+	/* Once for info->screen_base mmaping... */
> > >+	i915_gem_object_ggtt_unpin(obj);
> > >+	/* ...and once for the intel_fb */
> > >  	i915_gem_object_ggtt_unpin(obj);
> > >  	drm_gem_object_unreference(&obj->base);
> > >  out_unlock:
> > >@@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
> > >  static void intel_fbdev_destroy(struct drm_device *dev,
> > >  				struct intel_fbdev *ifbdev)
> > >  {
> > >+	/* Release the pinning for the info->screen_base mmaping. */
> > >+	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
> > >
> > >  	drm_fb_helper_unregister_fbi(&ifbdev->helper);
> > >  	drm_fb_helper_release_fbi(&ifbdev->helper);
> > 
> > Hmm .. pinning now done by i915_gem_obj_ggtt_pin(), but the unpinning
> > function is i915_gem_object_ggtt_unpin(). Just the sort of asymmetry that
> > helps everyone understand what's going on :(
> > 
> > Could we not have a mass rename of the various i915_gem_obj{ect} functions
> > to ONE consistent naming convention? (Personally I prefer 'obj' because it's
> > shorter, but consistency is more important than saving just 3 letters).
> 
> Of course, just needs someone to do it, and make sure to not step onto too
> many toes. I'd love if more people actually take charge of gem instead of
> piling more on top.

I have patches to remove as much of the nonsense as I could. I have sent
some of them before, but no one looked at them it seems. Now they are
about 150 patches from the top of the queue.
-Chris

Patch

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 6532912..0ad46521 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -215,6 +215,16 @@  static int intelfb_create(struct drm_fb_helper *helper,
 	obj = intel_fb->obj;
 	size = obj->base.size;
 
+	/* The fb constructor will have already pinned us (or inherited a
+	 * GGTT region from the BIOS) suitable for a scanout, so
+	 * this should just be a no-op and increment the pin count for the
+	 * fbdev mmapping. It does have a useful side-effect of validating
+	 * the pin for fbdev's use via a GGTT mmapping.
+	 */
+	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
+	if (ret)
+		goto out_unlock;
+
 	info = drm_fb_helper_alloc_fbi(helper);
 	if (IS_ERR(info)) {
 		ret = PTR_ERR(info);
@@ -274,6 +284,9 @@  static int intelfb_create(struct drm_fb_helper *helper,
 out_destroy_fbi:
 	drm_fb_helper_release_fbi(helper);
 out_unpin:
+	/* Once for info->screen_base mmaping... */
+	i915_gem_object_ggtt_unpin(obj);
+	/* ...and once for the intel_fb */
 	i915_gem_object_ggtt_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
 out_unlock:
@@ -514,6 +527,8 @@  static const struct drm_fb_helper_funcs intel_fb_helper_funcs = {
 static void intel_fbdev_destroy(struct drm_device *dev,
 				struct intel_fbdev *ifbdev)
 {
+	/* Release the pinning for the info->screen_base mmaping. */
+	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
 
 	drm_fb_helper_unregister_fbi(&ifbdev->helper);
 	drm_fb_helper_release_fbi(&ifbdev->helper);