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

From: Steve Longerbeam
Date: Sun Mar 12 2017 - 16:16:14 EST

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

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

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.