Re: [PATCH] drm/bridge: dw_hdmi: add cec notifier support

From: Russell King - ARM Linux
Date: Thu Jul 06 2017 - 07:57:19 EST

On Thu, Jul 06, 2017 at 12:45:55PM +0100, Russell King - ARM Linux wrote:
> Well, from what I can see in 4.12, the cec-notifier stuff is rather
> broken (tda998x has stopped working as its stuck with a physical
> address of f.f.f.f) so I think the whole thing is rather moot right
> now. I don't yet know what's going on with that, other than the
> notifier stuff seems to not be working, despite being enabled in
> the .config.

The problem there appears to be the changes that were made with the
way the config works - which IMHO are totally broken.

Let's take this scenario:

- You have a HDMI bridge, and you build that into the kernel, because you
want the display to come up early.
- You have a CEC driver, which you build as a module.

If the HDMI bridge driver selects CEC_NOTIFIER and the CEC driver selects
both CEC_NOTIFIER and CEC_CORE, you end up with CEC_NOTIFIER=y and

We now come to this:


The definition of IS_REACHABLE() is that it is false if the config symbol
is selected as a module. So, in this case, we end up compiling out all
the CEC notifier functions from the HDMI bridge, and building them into
the CEC driver.

The CEC notifier also gets built as a module, meaning that there's no way
for the built-in HDMI bridge could ever call the notifier.

The overall result of this is that such a configuration completely breaks
such a setup - a setup that worked fine before the CEC Kconfig changes.

This isn't limited to tda998x - I'd expect the same to be true of dw-hdmi.

RMK's Patch system:
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