[PATCH 4/4] drm/bridge: dw-hdmi: add cec driver
Hans Verkuil
hverkuil at xs4all.nl
Mon Jun 12 08:42:02 UTC 2017
On 06/01/2017 10:31 AM, Hans Verkuil wrote:
> Hi Russell,
>
> First a few top-level questions:
>
> 1) What was the reason for using the cec-notifier here? Isn't this
> tightly integrated into the main dw-hdmi block? For the tda driver
> it is clearly required, but for tightly coupled HDMI & CEC HW I
> just create the adapter from the HDMI driver. As a small bonus it
> avoids adding the cec-notifier code and the control flow is a bit
> easier to trace.
>
> 2) I may have asked this before, apologies if I repeat myself: does
> this CEC implementation support CEC monitoring (aka snooping)? If
> it does, then I recommend that it is implemented since it is very
> useful.
>
> 3) Is the CEC still active if there is no hotplug signal? Or is it
> powered off in that case? Ideally it should still be possible to
> send CEC messages even if there is no hotplug. This is explicitly
> allowed by the CEC 2.0 spec to wake up displays that turn off the
> HPD, but that still have a working CEC controller.
>
> If this is not possible, then you need to use the CEC_CAP_NEEDS_HPD
> capability. See: https://patchwork.linuxtv.org/patch/41478/
>
> This will almost certainly be merged for 4.13 since other CEC drivers
> need this as well.
FYI: I tested your patch series with my cubox-i and CEC doesn't work if there
is no HPD. I fiddles around a bit in dw_hdmi.c to prevent it from powering off
the HDMI and PHY, but without any luck. It could be a hardware issue on the
cubox-i (e.g. a level-shifter that powers off when the HPD goes low, although
I don't see anything like that in the schematics), or it can be a driver issue
or a Synopsys IP issue. I really can't tell.
I added text in my status document (https://hverkuil.home.xs4all.nl/cec-status.txt)
at the end on how to test this.
Otherwise the CEC support on the cubox-i was working very well.
Regards,
Hans
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