From: srinivas.kandagatla@linaro.org (Srinivas Kandagatla)
To: linux-arm-kernel@lists.infradead.org
Subject: a case for a common efuse API?
Date: Wed, 09 Jul 2014 08:50:59 +0100 [thread overview]
Message-ID: <53BCF463.3000604@linaro.org> (raw)
In-Reply-To: <53BC4DD7.20906@codeaurora.org>
On 08/07/14 21:00, 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>;
> }
>
>
> Where we can point to the efuse and give an address offset. From code we
> could then call some efuse_read() function to read the sensor's
> calibration data.
>
> It's been suggested that we use syscon for this, but I wonder if that is
> the right thing to do. With a syscon you're usually writing some
> registers that got lumped together with other registers that aren't
> directly related to your driver. It doesn't seem like syscon is made for
> reading fuses or other things like eeproms. Maybe I'm wrong though.
>
I remember there was a similar discussion some time last year about
this: https://lkml.org/lkml/2013/7/5/361
> Using syscon would probably work if we could add a way to point to
> offsets within the syscon node (the 0x18 part in the example). In my
> specific use-case the calibration data may have different offsets
> depending on which SoC the hardware is instantiated in so we could also
> make syscon work if the compatible field for the sensor node indicates
> which SoC it is.
Something like this:
efuse: efuse at 10000 {
compatible = "efuse", "syscon";
reg = <0x10000 0x1000>;
}
thermal-sensor at 34000 {
compatible = "sensor", "soc-xyz";
reg = <0x34000 0x1000>;
syscon = <&efuse>;
}
sensor driver could add of_data for the soc-xyz which would contain soc
specific efuse offsets.
--srini
>
> I added Tegra folks because I see that on Tegra this hardware is exposed
> via an SoC specific API, tegra_fuse_readl(), and an associated driver in
> drivers/misc/fuse/tegra/. Unfortunately I don't see any users of the API
> outside of the speedo code in the same directory and the sysfs bin
> attribute that may or may not be in use by some userspace code.
>
next prev parent reply other threads:[~2014-07-09 7:50 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-08 20:00 a case for a common efuse API? Stephen Boyd
2014-07-08 20:26 ` Olof Johansson
2014-07-08 21:59 ` Bjorn Andersson
2014-07-09 7:24 ` Uwe Kleine-König
2014-07-09 7:50 ` Srinivas Kandagatla [this message]
2014-07-09 8:35 ` Maxime Ripard
2014-07-09 23:32 ` Stephen Boyd
2014-07-10 14:26 ` Maxime Ripard
2014-07-10 15:18 ` Alexandre Belloni
2014-07-10 15:41 ` Grygorii Strashko
2014-07-10 15:09 ` Maxime Ripard
2014-09-11 21:59 ` Stephen Boyd
2014-09-16 10:16 ` Maxime Ripard
2014-07-09 11:49 ` Peter De Schrijver
2014-07-21 15:51 ` Stephen Warren
2014-07-09 20:42 ` Tomasz Figa
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