From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 7/7] ARM: tegra: Add the EC i2c tunnel to tegra124-venice2 Date: Mon, 21 Apr 2014 14:03:49 -0600 Message-ID: <535579A5.2060603@wwwdotorg.org> References: <1397757570-19750-1-git-send-email-dianders@chromium.org> <1397757570-19750-8-git-send-email-dianders@chromium.org> <535560E9.5040108@wwwdotorg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-samsung-soc-owner@vger.kernel.org To: Doug Anderson Cc: Lee Jones , Stephen Warren , Wolfram Sang , Andrew Bresticker , Dylan Reid , Olof Johansson , Simon Glass , linux-samsung-soc , "linux-tegra@vger.kernel.org" , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Russell King , Thierry Reding , "devicetree@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" List-Id: linux-tegra@vger.kernel.org On 04/21/2014 01:35 PM, Doug Anderson wrote: > Stephen, > > On Mon, Apr 21, 2014 at 11:18 AM, Stephen Warren wrote: >> On 04/17/2014 11:59 AM, Doug Anderson wrote: >>> This adds the EC i2c tunnel (and devices under it) to the >>> tegra124-venice2 device tree. >>> diff --git a/arch/arm/boot/dts/tegra124-venice2.dts b/arch/arm/boot/dts/tegra124-venice2.dts >> >>> aliases { >>> + i2c20 = "/spi@0,7000d400/cros-ec@0/i2c-tunnel"; >> >> Is that needed? I'd prefer not to add it unless there's a specific >> reason. I don't think I2C buses need specific names, do they? > > It is not strictly needed, but from a usability standpoint it is > terribly helpful. It serves to make it obvious to someone looking at > the device that it's _not_ an i2c bus associated with the main SoC. > If you don't include a number I believe that the i2c core will pick > the first available number. > > It seems worth it to save a few people a few hours of head scratching. > > ...but this is your dts and if you think it's a terrible idea then > I'll remove it. It looks to be less critical on tegra than it is on > exynos (which has ~9 i2c busses, they are numbered in the user manual, > and if you have one set to "disable" in the dts then the tunnel will > end up getting a very confusing number). My opinion is that the in-kernel I2C bus numbering is an entirely unrelated numbering space to the HW controller numbering space precisely because of issues like that. DT aliases are more useful for user-visible port numbering (e.g. HDMI 0, 1 connectors on a case) than purely internal details like this. So, I would leave it out.