[PATCH 2/4] ARM i.MX: add SoC type detection for i.MX6SL

[Alexander Kurz]

On Wed, 7 Dec 2016, Sascha Hauer wrote:

> Hi Alexander,
> 
> On Mon, Nov 28, 2016 at 10:27:33AM +0100, Alexander Kurz wrote:
> > The i.MX6 series SoC type is determined by barebox by examining the
> > USB_ANALOG_DIGPROG aka IMX6_ANATOP_SI_REV register. This register is located
> > at a common offset for all mx6 SoC - except for i.MX6SL where a different
> > offset is used. This creates a dilemma while distinguishing the mx6sl from
> > non-mx6sl SOC since the SoC type identification register location is type
> > specific itself.
> > 
> > Access to undocumented and probably invalid or unpredictable registers should
> > be avoided as possible. For the mx6sl detection an access to the general
> > USB_ANALOG_DIGPROG @0x260 cannot be avoided when running on mx6sl. This
> > register contained the value 0x00014009 for different mx6sl Rev. 1.2 based
> > e-book readers using MCIMX6L7DVN10AB and MCIMX6L8DVN10AB SoC. This
> > implementation assumes the value of MAJOR_UPPER (here 0x01) to be smaller
> > than the smallest non-6sl MAJOR_UPPER (0x61 for mx6s).
> 
> The i.MX6SL code would be quite straight forward and easy to merge
> without this handicap. I'll probably need a few more days to swallow
> this pill. I assume you already searched for better ways to detect a
> i.MX6SL, right?
>
The uboot-implementation (get_cpu_rev() in arch/arm/cpu/armv7/mx6/soc.c)
first checks the 6SL-digprog register and then proceeds with the non-6SL 
detection. This results in access to non-documented registers for all 
non-6SL SoC. My implementation limits potential trouble to 6SL and any
SoC not detected yet.

I did not find any good hint in the reference manuals, but anyway, if
it would exist, I would assume it to be used in the freescale u-boot 
branch (which is similar to mainline u-boot).

Regards, Alexander
> 
> Sascha
> 
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