linux-kernel - Re: [PATCH 4/6] nvmem: sunxi_sid: Read out data in native format

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Date:   Mon, 18 Mar 2019 17:09:44 +0800
From:   Chen-Yu Tsai <wens@...nel.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] nvmem: sunxi_sid: Read out data in native format

On Mon, Mar 18, 2019 at 4:57 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Mon, Mar 18, 2019 at 04:45:19PM +0800, Chen-Yu Tsai wrote:
> > On Mon, Mar 18, 2019 at 4:42 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > >
> > > Hi,
> > >
> > > On Mon, Mar 18, 2019 at 03:33:52PM +0800, Chen-Yu Tsai wrote:
> > > > From: Chen-Yu Tsai <wens@...e.org>
> > > >
> > > > Originally the SID e-fuses were thought to be in big-endian format.
> > > > Later sources show that they are in fact native or little-endian.
> > > > The most compelling evidence is the thermal sensor calibration data,
> > > > which is a set of one to three 16-bit values. In native-endian they
> > > > are in 16-bit cells with increasing offsets, whereas with big-endian
> > > > they are in the wrong order, and a gap with no data will show if there
> > > > are one or three cells.
> > > >
> > > > Switch to a native endian representation for the nvmem device. For the
> > > > H3, the register read-out method was already returning data in native
> > > > endian. This only affects the other SoCs.
> > > >
> > > > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > >
> > > I thought only the newer SoCs were impacted by this issue?
> >
> > It is noticable on the newer SoCs. The old ones only have the 128-bit SID,
> > which could be read either way, as AFAIK it's just a serial number.
> >
> > If you think we should leave the old ones alone I can factor that in.
>
> IIRC, there was also the SoC ID in the SID on those SoCs as well,
> which we might have to use in the future so we'll want to make sure it
> is correct.

We'll need to ask Allwinner about this then.

FWIW, the fel command in sunxi-tools reads them out in little endian. I
believe this and the SID page on the linux-sunxi wiki predate the sunxi_sid
driver.

ChenYu