Re: [PATCH v2 27/27] drm/tegra: Add Tegra114 gr2d support

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Mon, Oct 14, 2013 at 08:58:34AM +0300, Terje Bergström wrote:
> On 12.10.2013 01:43, Stephen Warren wrote:
> > On 10/07/2013 02:34 AM, Thierry Reding wrote:
> >> The gr2d hardware in Tegra114 is compatible with that of Tegra20 and
> >> Tegra30. No functionaly changes are required.
> > Similarly here, if the HW is 100% backwards-compatible, there's no need
> > to add compatible values to the driver.
> 
> We've used this mechanism for attaching a per-hw-version data structure
> in match table to accomodate differences in how the hardware is power
> gated, reset, booted, some per-soc performance related changes etc. It's
> also used in staging features for new chips, such as disabling power
> features when they're not working/verified yet.
> 
> Upstream driver is not yet in a state where that is relevant.
> 
> With this, would we still be able to do that with match table? It sounds
> like we could, because we can still (even with multiple compatible
> properties) add separate entries in match table and I guess the
> compatible properties matched in order.

Yes, as long as the device tree files includes the most specific value
in the compatible this should still be possible. So we'd have this:

	gr2d@54140000 {
		compatible = "nvida,tegra114-gr2d", "nvidia,tegra20-gr2d";
		...
	};

and the driver will match on "nvidia,tegra20-gr2d" if the more specific
"nvidia,tegra114-gr2d" is not there. When the driver is updated to
support Tegra114 specific functionality, then a more specific entry can
be added to the compatible table to handle it.

Thierry

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