From mboxrd@z Thu Jan 1 00:00:00 1970 From: maxime.ripard@free-electrons.com (Maxime Ripard) Date: Thu, 10 Jul 2014 16:26:16 +0200 Subject: a case for a common efuse API? In-Reply-To: <53BDD0F3.7040906@codeaurora.org> References: <53BC4DD7.20906@codeaurora.org> <20140709083509.GQ13423@lukather> <53BDD0F3.7040906@codeaurora.org> Message-ID: <20140710142616.GD27469@lukather> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 at 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 at 10000 { > >> compatible = "efuse"; > >> reg = <0x10000 0x1000>; > >> } > >> > >> thermal-sensor at 34000 { > >> compatible = "sensor"; > >> reg = <0x34000 0x1000>; > >> efuse = <&efuse 0x18>; > >> } > > 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. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: