[Intel-gfx] [PATCH] drm/i915: Clarify the safety of the early unpin of old_fb->obj

[Chris Wilson]

On Tue, May 20, 2014 at 08:47:41AM +0100, Chris Wilson wrote:
> Daniel simplified the modesetting code to push the common work performed
> by each of the architecture specific routines higher into the caller. This
> took me a while to be sure that it was safe in the event of a
> modesetting failure - to be sure that the dangling pointer we left in
> the registers would never be accessed. As it turns out, it is safe, as
> even after the most convoluted error path, we always rewrite the address
> registers with the currently pinned object before enabling the planes
> and pipes. This patch just adds an assertion that the preconditions
> Daniel stated are correct, and a comment to justify the dance.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 30 ++++++++++++++++++++++--------
>  1 file changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 28f31145335d..907ed158c676 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -1193,7 +1193,7 @@ static void assert_cursor(struct drm_i915_private *dev_priv,
>  #define assert_cursor_enabled(d, p) assert_cursor(d, p, true)
>  #define assert_cursor_disabled(d, p) assert_cursor(d, p, false)
>  
> -void assert_pipe(struct drm_i915_private *dev_priv,
> +bool assert_pipe(struct drm_i915_private *dev_priv,
>  		 enum pipe pipe, bool state)

Sigh. I forgot this is now exported.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre