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: Tue, 15 Oct 2013 09:12:46 -0600 Message-ID: <525D5B6E.30301@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> <525C3497.6010700@wwwdotorg.org> <525CD7F3.10907@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <525CD7F3.10907-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: =?UTF-8?B?VGVyamUgQmVyZ3N0csO2bQ==?= , Thierry Reding 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 11:51 PM, Terje Bergstr=C3=B6m wrote: > On 14.10.2013 21:14, Stephen Warren wrote: >> On 10/14/2013 08:00 AM, Thierry Reding wrote: >>> 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 =3D "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. >> >> 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. >=20 > I don't know of any hardware incompatibility. The only difference is > related to something not directly to 2D. We moved host1x away from th= e > power domain, so in Tegra114 we're able to power gate 2D and EPP. The > DVFS tables are also different. >=20 > I'd say say adding the compatible property "nvidia,tegra20-gr2d" for > Tegra114's 2D is accurate and we're able to use the match table to dr= ive > any SW policy differences. The compatible value shouldn't be used for SW policy differences. DT is about HW, not SW policy. You have to decide: either the HW is 100% backwards-compatible, or it's not. You can't decide that the HW is compatible, but then require different compatible values.