From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH v2 27/27] drm/tegra: Add Tegra114 gr2d support Date: Mon, 14 Oct 2013 12:14:47 -0600 Message-ID: <525C3497.6010700@wwwdotorg.org> References: <1381134884-5816-1-git-send-email-treding@nvidia.com> <1381134884-5816-28-git-send-email-treding@nvidia.com> <52587F2D.9070007@wwwdotorg.org> <525B880A.7090802@nvidia.com> <20131014140010.GC16302@ulmo.nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20131014140010.GC16302-AwZRO8vwLAwmlAP/+Wk3EA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Thierry Reding , =?UTF-8?B?VGVyamUgQmVyZ3N0?= =?UTF-8?B?csO2bQ==?= Cc: "dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: devicetree@vger.kernel.org On 10/14/2013 08:00 AM, Thierry Reding wrote: > On Mon, Oct 14, 2013 at 08:58:34AM +0300, Terje Bergstr=C3=B6m 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. >>=20 >> 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. >>=20 >> Upstream driver is not yet in a state where that is relevant. >>=20 >> 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. >=20 > 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: >=20 > gr2d@54140000 { compatible =3D "nvida,tegra114-gr2d", > "nvidia,tegra20-gr2d"; ... }; >=20 > 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. True, but the DT fragment above is also only accurate /if/ a driver that only knows about "nvidia,tegra20-gr2d" can operate 100% of the features in Tegra20 HW on Tegra114 HW forever.