[bug report] drm/vc4: dsi: Fix bridge chain handling

[Dan Carpenter]

On Wed, Jun 24, 2020 at 08:30:25PM +0200, Boris Brezillon wrote:
> Hello Dan,
> 
> On Wed, 24 Jun 2020 20:58:06 +0300
> Dan Carpenter <dan.carpenter at oracle.com> wrote:
> 
> > Hello Boris Brezillon,
> > 
> > The patch 033bfe7538a1: "drm/vc4: dsi: Fix bridge chain handling"
> > from Dec 27, 2019, leads to the following static checker warning:
> > 
> > 	drivers/gpu/drm/vc4/vc4_dsi.c:758 vc4_dsi_encoder_disable()
> > 	warn: iterator used outside loop: 'iter'
> > 
> > drivers/gpu/drm/vc4/vc4_dsi.c
> >    743  static void vc4_dsi_encoder_disable(struct drm_encoder *encoder)
> >    744  {
> >    745          struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
> >    746          struct vc4_dsi *dsi = vc4_encoder->dsi;
> >    747          struct device *dev = &dsi->pdev->dev;
> >    748          struct drm_bridge *iter;
> >    749  
> >    750          list_for_each_entry_reverse(iter, &dsi->bridge_chain, chain_node) {
> >    751                  if (iter->funcs->disable)
> >    752                          iter->funcs->disable(iter);
> >    753          }
> > 
> > This loops backwards until iter is parked on the list head.
> > 
> >    754  
> >    755          vc4_dsi_ulps(dsi, true);
> >    756  
> >    757          list_for_each_entry_from(iter, &dsi->bridge_chain, chain_node) {
> > 
> > But then this "continues" until the iter is parked on the list head.
> > Since we ended with the iterator already on the list head then we never
> > enter this loop and it is a no-op.
> > 
> > Am I missing something?
> 
> It should definitely be list_for_each_entry() here. Thanks for
> this report. Would you mind sending a patch?

Yeah.  I can do that tomorrow.

I'm working on a new Smatch check and so I wasn't super familiar with
some of these list_for_each() loops.  Thanks!

regards,
dan carpenter