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

[Steve Longerbeam <slongerbeam@gmail.com>]

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
>