[PATCH] drm: Always prepare null framebuffer in transitional helper

[Daniel Vetter]

On Sun, Feb 26, 2017 at 09:57:16PM +0100, Daniel Vetter wrote:
> On Thu, Feb 16, 2017 at 02:44:42PM -0200, Gabriel Krisman Bertazi wrote:
> > Despite the documentation claim that cleanup_fb will match prior calls
> > to prepare_fb, in case of NULL framebuffers in the transitional helpers,
> > the code will skip the call to prepare_fb but not the corresponding
> > cleanup_fb call.  This asymmetry in semantics is unnecessarily surprising
> > for developers transitioning drivers to atomic model, specially because
> > the final atomic handlers don't have the issue - the prepare_fb is
> > always called, despite the new state framebuffer being null.
> > 
> > The only current user of the transitional helper that doesn't take care
> > of null framebuffers explicitly inside the prepare_fb hook is
> > atmel_hlcdc, so we take special care to make sure we don't break
> > anything there.
> 
> Oh dear, I noticed all the callers to drm_plane_helper_disable :( What
> they really all want to do is shut down the entire display pipe on driver
> unload, with drm_atomic_helper_disable_all().
> 
> A bit more work to do in a simple cleanup, but care to at least do a small
> patch to Documentation/gpu/todo.rst to note it?

Patch itself applied to drm-misc, thanks.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch