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

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Message-ID: <20190318092519.g2rvdjiunti2ev7p@flea>
Date:   Mon, 18 Mar 2019 10:25:19 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...nel.org>
Cc:     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 05:09:44PM +0800, Chen-Yu Tsai wrote:
> 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.

Yeah, and the driver has a readl as well:
https://github.com/linux-sunxi/linux-sunxi/blob/sunxi-3.4/arch/arm/plat-sunxi/soc-detect.c#L92

For the whole series,
Acked-by: Maxime Ripard <maxime.ripard@...tlin.com>

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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