Re: exynos4412: powerdomain issues with HDMI PHY and VP

[Kevin Hilman <khilman@linaro.org>]

Tomasz Figa <tomasz.figa@gmail.com> writes:

> Hi Tobias,
>
> First of all, big thanks for investigating this issue. Hopefully we can
> have it fixed in upstream soon.
>
> I've added Tomasz Stanislawski to CC list, as he's been doing some work
> to enable HDMI support on Exynos4 using Exynos DRM.
>
> On 24.05.2014 22:45, Tobias Jakobi wrote:
>> Hello,
>> 
>> I'm still working on getting HDMI output on my ODROID-X2 board (based on
>> Exynos4412 Prime) working. My tree is a 3.15-rc6 with some patches on
>> top to get it boot on the board.
>> 
>> You can find the tree here:
>> https://github.com/tobiasjakobi/linux-odroid/commits/odroid-3.15.y
>> 
>> Here is the DTS:
>> https://github.com/tobiasjakobi/linux-odroid/blob/odroid-3.15.y/arch/arm/boot/dts/exynos4412-odroidx2.dts
>> 
>> I encountered two issues with powerdomains. On related to HDMI PHY and
>> the other one related to the VP (video processor).
>> 
>> The pd the mixer is in, is currently set to pd_tv. I can't seem to
>> specify multiple powerdomains for one device. However the PHY seems to
>> need both TV and LCD0 pd to function properly.
>
> We've discovered this issue too. Unfortunately the Linux implementation
> of generic power domain core (genpd) doesn't support multiple power
> domains per device, so we ended up with a hack in our internal tree.
>
> Generic power domain bindings aren't going to help too much, because
> even though they account for this, the implementation will use only the
> first domain.
>
> I have CC'ed Rafael, Kevin and Ulf, as they might have some ideas how to
> solve this.

Hmm, this seems a bit strange.  How is this implemented in hardware?  It
seems rather unlikely that the same IP block is getting power from two
different power rails.  So I don't think what you really want is to have
the device modeled in 2 power domains.

Rather, I suspect there's some functional dependency going on that's not
directly a function of the power domain itself.  Taking a wild shot in
the dark, it wouldn't be too surprising if the IP block in question
depends on a clock coming from a device in another power domain?  Since
this sounds display related, is the pixel clock required coming from an
IP block in the other power domain?

If it's something like a clock dependency, then that needs to be modeled
so what when the clock is enabled, the power domain containg the device
providing that clock cannot be shut down.

Kevin