Re: [PATCH v5 00/39] i.MX Media Driver

[Steve Longerbeam]

On 03/12/2017 01:36 PM, Steve Longerbeam wrote:
> On 03/12/2017 01:16 PM, Steve Longerbeam wrote:
> > On 03/12/2017 12:44 PM, Steve Longerbeam wrote:
> > > On 03/12/2017 12:29 PM, Russell King - ARM Linux wrote:
> > > > On Sun, Mar 12, 2017 at 12:21:45PM -0700, Steve Longerbeam wrote:
> > > > > There's actually nothing preventing userland from disabling a link
> > > > > multiple times, and imx_media_link_notify() complies, and so
> > > > > csi_s_power(OFF) gets called multiple times, and so that WARN_ON()
> > > > > in there is silly, I borrowed this from other MC driver examples,
> > > > > but it makes no sense to me, I'll remove it and prevent the power
> > > > > count from going negative.
> > > >
> > > > Hmm.  So what happens if one of the CSI's links is enabled, and we
> > > > disable a different link from the CSI several times?  Doesn't that
> > > > mean the power count will go to zero despite there being an enabled
> > > > link?
> > >
> > > Yes, the CSI will be powered off even if it still has an enabled link.
> > > But one of its other links has been disabled, meaning the pipeline as
> > > a whole is disabled. So I think it makes sense to power down the CSI,
> > > the pipeline isn't usable at that point.
> > >
> > > And remember that the CSI does not allow both output pads to be enabled
> > > at the same time. If that were so then indeed there would be a problem,
> > > because it would mean there is another active pipeline that requires the
> > > CSI being powered on, but that's not the case.
> > >
> > > I think this is consistent with the other entities as well, but I will
> > > double check.
> >
> >
> > At first I thought this could be a problem for one entity, the csi-2
> > receiver.
> >
> > It can enable all four of its output pads at once (if the input stream
> > contains all 4 virtual channels, the csi-2 receiver must support
> > demuxing all of them onto all 4 of its output pads).
> >
> > But after more review, this should not be an issue. If a csi-2 sink
> > (a CSI or a CSI mux) link is disabled, the csi-2 receiver is no longer
> > reachable from that sink, so attempts to disable the csi-2 via that
> > path again is not possible. The other potential problem is disabling
> > from the csi-2's own sink pad, but in that case the csi-2 no longer
> > has a source, so again it makes sense to power off the csi-2 even
> > if it has enabled output pads.
>
> But hold on, if my logic is correct, then why did the CSI power-off
> get reached in your case, multiple times? Yes I think there is a bug,
> link_notify() is not checking if the link has already been disabled.
> I will fix this. But I'm surprised media core's link_notify handling
> doesn't do this.

but it does:

int __media_entity_setup_link(struct media_link *link, u32 flags)
{
...
    if (link->flags == flags)
        return 0;
...
}

What the heck. Anyway, I'll track this down.

Steve

> Steve