Re: [RFC v2 6/8] gpu: drm: tegra: Remove redundant host1x

From: Terje BergstrÃm
Date: Mon Jan 07 2013 - 03:15:07 EST

On 04.01.2013 22:25, Stephen Warren wrote:
> On 01/04/2013 03:09 AM, Terje BergstrÃm wrote:
> ...
>> I think we have now two ways to go forward with cons and pros:
>> 1) Keep host1x and tegra-drm as separate driver
>> + Code almost done
>> - we need dummy device and dummy driver
>> - extra code and API when host1x creates dummy device and its passed
>> to tegra-drm
> Just to play devil's advocate:
> I suspect that's only a few lines of code.

Yes, that's true. There's some overhead, but there's not too many actual
code lines.

>> - tegra-drm device would need to be a child of host1x device. Having
>> virtual and real devices as host1x children sounds weird.
> And I doubt that would cause problems.

True. It could become a problem if the driver just assumed that all
host1x children are actual hardware, but we could avoid that.

>> 2) Merge host1x and tegra-drm into one module. drm is a subcomponent,
>> and whatever other personalities we wish would also be subcomponents of
>> host1x. host1x calls tegra-drm directly to handle preparation for drm
>> initialization. As they're in the same module, circular dependency is ok.
>> + Simpler conceptually (no dummy device/driver)
>> + Less code
>> - Proposal doesn't yet exist
> But that said, I agree this approach would be very reasonable; it seems
> to me that host1x really is the main HW behind a DRM driver or a V4L2
> driver or ... As such, it seems quite reasonable for a single struct
> device to exist that represents host1x, and for the driver for that
> device to register both a DRM and a V4L2 driver etc. The code could
> physically be organized into separate modules, and under different
> Kconfig options for configurability etc.
> But either way, I'll let you (Thierry and Terje) work out which way to go.

If we want separate modules, we'd need the dummy device & dummy driver
binding between them. We could also just put them in the same module.
It'd make DRM a requirement to host1x driver, but given the current
structure, I think that'd be reasonable. We could later make it more
configurable if needed. Does this now make tegra-drm and host1x too
dependent on each other? I'm not sure.

I also like the fact that we don't have to export APIs to include, but
we can (if we so choose) keep all tegra-drm-host1x-APIs in local header
files. As we have noted, the two drivers are tightly interconnected,
changing the APIs is easier if we can just work on the same directory

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