Problems to Allwinner H3's eFUSE/SID

[Hans de Goede]

Hi,

On 19-12-16 17:06, Icenowy Zheng wrote:
>
>
> 19.12.2016, 23:30, "Hans de Goede" <hdegoede at redhat.com>:
>> Hi,
>>
>> On 19-12-16 16:22, Icenowy Zheng wrote:
>>>  Hi everyone,
>>>
>>>  Today, I and KotCzarny on IRC of linux-sunxi found a problem in the SID
>>>  controller of H3 (incl. H2+).
>>>
>>>  See https://irclog.whitequark.org/linux-sunxi/2016-12-19 .
>>>
>>>  Two read method of the H3 eFUSE is used in the BSP: by register accessing, or
>>>  directly access 0x01c14200.
>>>
>>>  From http://linux-sunxi.org/SID_Register_Guide we can see a difference between
>>>  the H3 SIDs read out by sunxi-fel and the H3 SIDs read out by devmem2 (in
>>>  legacy kernel).
>>>
>>>  According to the source of H2+ BSP[1], H2+ and H3 can be differed by the last
>>>  byte of the first word of SID. (0x42 and 0x83 is H2+, 0x00 and 0x81 is H3,
>>>  0x58 is H3D (currently not known SoC) )
>>>
>>>  However, all the SIDs retrieved by `sunxi-fel sid`, both H2+ and H3, start
>>>  with 0x02004620, which do not match this rule.
>>>
>>>  The readout by devmem2 is satisfying this rule: their first word is
>>>  0x02c00081, matches H3.
>>>
>>>  Then I found the SID-reading code from BSP U-Boot[2], which is based on
>>>  register operations. With this kind of code (I wrote one prototype in
>>>  userspace with /dev/mem), I got "02c00081 74004620 50358720 3c27048e" on
>>>  my Orange Pi One. ("02004620 74358720 5027048e 3c0000c3" with sunxi-fel sid)
>>>  And, after accessing to the SID by registers, the value of *0x01c14200 become
>>>  also "02c00081".
>>>
>>>  With direct access to 0x01c14200 after boot with mainline kernel, I got also
>>>  "02004620".
>>>
>>>  Then I altered the program to do the register operations with sunxi-fel, the
>>>  result is also "02c00081", and changed `sunxi-fel sid` result to "02c00081".
>>>
>>>  Summary:
>>>
>>>  +-----------------------------------------------+----------------+
>>>  | Read situation | The first word |
>>>  +-----------------------------------------------+----------------+
>>>  | Direct read by sunxi-fel | 02004620 |
>>>  | Direct read in mainline /dev/mem | 02004620 |
>>>  | Direct read in legacy /dev/mem | 02c00081 |
>>>  | Register access in FEL | 02c00081 |
>>>  | Register access in mainline | 02c00081 |
>>>  | Direct read after register access in FEL | 02c00081 |
>>>  | Direct read after register access in mainline | 02c00081 |
>>>  +-----------------------------------------------+----------------+
>>>
>>>  According to some facts:
>>>  - The register based access to SID is weird: it needs ~5 register
>>>    operations per word of SID.
>>>  - Reading via register access will change the value when reading by accessing
>>>    0x01c14200.
>>>  - In the u-boot code[2] there's some functions which read out the SID by
>>>    registers and then abandoned the value.
>>>  - This mismatch do not exist on A64.
>>>
>>>  I think that: Allwinner designed a "cache" to the SID to make the simplify the
>>>  code to read it, and it automatically loaded the cache when booting; however,
>>>  when doing first cache on H3, some byte shifts occured, and the value become
>>>  wrong. A manual read on H3 can make the cache right again. This is a silicon
>>>  bug, and fixed in A64.
>>>
>>>  This raises a problem: currently many systems has used the misread SID value to
>>>  generated lots of MAC addresses, and workaround this SID bug will change them.
>>>
>>>  However, if this bug is not workarounded, the sun8i-ths driver won't work well
>>>  (as some calibartion value lies in eFUSE). I think some early user of this
>>>  driver has already experienced bad readout value.
>>>  (The calibration value differs on my opi1 and KotCzarny's opipc)
>>>
>>>  And many wrong SID values have been generated by `sunxi-fel sid`. (Although I
>>>  think sunxi-fel must have the workaround)
>>>
>>>  Note: in this email, "SID" and "eFUSE" both indicate the controller on H3/A64
>>>  at 0x01c14000, which is a OTP memory implemented by eFUSE technique.
>>>
>>>  Furthermore, A83T may also have this problem, testers are welcome!
>>>
>>>  [1] http://filez.zoobab.com/allwinner/h2/201609022/lichee/linux-3.4/arch/arm/mach-sunxi/sun8i.c
>>>  [2] http://filez.zoobab.com/allwinner/h2/201609022/lichee/brandy/u-boot-2011.09/arch/arm/cpu/armv7/sun8iw7/efuse.c
>>>
>>>  Experiments:
>>>  - https://gist.github.com/Icenowy/2f4859ab1bc05814522fc7445179a8c9
>>>    A SID readout shell script via FEL with register access.
>>>  - https://31.135.195.151:20281/d/efuse/
>>>    A SID readout program via /dev/mem with register access by KotCzarny.
>>>    (with statically compiled binary)
>>
>> Good detective work!
>>
>> I believe this would best be fixed by making u-boot use the register access
>> method to get the SID on affected chips, and make sure u-boot reads the
>> SID at-least once.
>
> Yes.
>
> However, what I considered is that fixing this bug will change H3 devices'
> MAC addresses, as they are derived from SID.

I know, but I think we will just need to accept this onetime change
of the fixed MAC addresses to fix this bug. I don't think this is
a big problem since the driver for the H3 ethernet has not been
merged into the mainline kernel yet.

> Maybe we should add #ifdef's to MAC generation code after this fix.

I would rather not see #ifdefs for this, see above, but that is no
longer my call, see below.

>
> (This is why I will create this discussion)
>
> P.S. Are you still the maintainer of sunxi boards support of u-boot? The
> MAINTAINER file in board/sunxi indicates this.

No I'm no longer the maintainer, I'm still the MAINTAINER file because
I have a lot of boards and as such I'm still the point of contact for
those boards (if there are any board specific issues / questions), but
as indicated in the main MAINTAINERS file Jagan Teki <jagan at openedev.com>
is the maintainer now.

Regards,

Hans