From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grygorii Strashko Subject: Re: a case for a common efuse API? Date: Thu, 10 Jul 2014 18:41:55 +0300 Message-ID: <53BEB443.9000606@ti.com> References: <53BC4DD7.20906@codeaurora.org> <20140709083509.GQ13423@lukather> <53BDD0F3.7040906@codeaurora.org> <20140710142616.GD27469@lukather> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140710142616.GD27469@lukather> Sender: linux-kernel-owner@vger.kernel.org To: Maxime Ripard , Stephen Boyd Cc: "devicetree@vger.kernel.org" , Stephen Warren , Arnd Bergmann , "linux-arm-msm@vger.kernel.org" , Peter De Schrijver , Linux Kernel Mailing List , Bjorn Andersson , "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org On 07/10/2014 05:26 PM, Maxime Ripard wrote: > On Wed, Jul 09, 2014 at 04:32:03PM -0700, Stephen Boyd wrote: >> On 07/09/14 01:35, Maxime Ripard wrote: >>> Hi Stephen, >>> >>> On Tue, Jul 08, 2014 at 01:00:23PM -0700, Stephen Boyd wrote: >>>> Hi, >>>> >>>> On MSM chips we have some efuses (called qfprom) where we store things >>>> like calibration data, speed bins, etc. We need to read out data from >>>> the efuses in various drivers like the cpufreq, thermal, etc. This >>>> essentially boils down to a bunch of readls on the efuse from a handful >>>> of different drivers. In devicetree this looks a little odd because >>>> these drivers end up having an extra reg property (or two) that points >>>> to a register in the efuse and some length, i.e you see this: >>>> >>>> thermal-sensor@34000 { >>>> compatible = "sensor"; >>>> reg = <0x34000 0x1000>, <0x10018 0xc>; >>>> reg-names = "sensor", "efuse_calib"; >>>> } >>>> >>>> >>>> I imagine in DT we want something more like this: >>>> >>>> efuse: efuse@10000 { >>>> compatible = "efuse"; >>>> reg = <0x10000 0x1000>; >>>> } >>>> >>>> thermal-sensor@34000 { >>>> compatible = "sensor"; >>>> reg = <0x34000 0x1000>; >>>> efuse = <&efuse 0x18>; >>>> } Why don't use "syscon" framework for your needs? (mfd/syscon.c) >>> We have pretty much the same things in the Allwinner SoCs. We have an >>> efuse directly mapped into memory, with a few informations like a MAC >>> address, the SoC ID, the serial number, some RSA keys for the device, >>> etc. >>> >>> The thing is, some boards expose these informations in an external >>> EEPROM as well. >>> >>> I started working and went quite far to create an "eeprom" framework >>> to handle these cases, with a dt representation similar to what you >>> were exposing. >>> >>> https://github.com/mripard/linux/tree/eeprom-framework-at24 >>> >>> It was working quite well, I was about to send it, but was told that I >>> should all be moved to MTD, and given up on it. >> >> Did anything ever get merged? Or the whole thing was dropped? > > Nope, I just never posted it. I could send it as an RFC though, and > see what are the feedbacks. > >> That branch looks like what I want, assuming we could get an agreement >> on the binding. It looks like pretty much every SoC has this, and there >> isn't any API or binding for it that I've seen. The only thing I see is >> Documentation/devicetree/bindings/eeprom.txt and that doesn't cover the >> client aspect at all. >> >> Taking a quick peek at the code, it might be better to change the read >> API to take a buffer and length, so that the caller doesn't need to free >> the data allocated by the eeprom layer. It also makes it symmetrical >> with the write API. We'd probably also need to make it work really early >> for SoC's like Tegra where we want to read the SoC revision early. So >> probably split off the device registration part to a later time to allow >> register() to be called early. > > I guess that the kind of things we could discuss after posting these > patches, but yep, it looks reasonnable. > > I'll try to get things a bit cleaner, and post them in the next days. > Regards, -grygorii