Hi, On 10/07/2014 at 16:26:16 +0200, 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>; > > >> } > > > 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. > Be aware that some SoCs are storing their OPPs there so this would be useful if that framework is available early enough to register those to cpufreq. -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html