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

Steve Longerbeam slongerbeam at gmail.com
Sun Mar 12 13:36:32 PDT 2017

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.


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