linux-kernel - Re: [RFC PATCH 0/1] Timeout error with Microchip OTPC driver on SAM9X60

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Message-ID: <20240813-payable-ecology-8a9e739704bb@thorsis.com>
Date: Tue, 13 Aug 2024 10:55:37 +0200
From: Alexander Dahl <ada@...rsis.com>
To: claudiu beznea <claudiu.beznea@...on.dev>
Cc: Alexander Dahl <ada@...rsis.com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: Re: [RFC PATCH 0/1] Timeout error with Microchip OTPC driver on
 SAM9X60

Hello Claudiu,

Am Wed, Apr 24, 2024 at 10:32:02AM +0300 schrieb claudiu beznea:
> Hi, Alexander,
> 
> On 12.04.2024 17:08, Alexander Dahl wrote:
> > Hei hei,
> > 
> > on a custom sam9x60 based board we want to access a unique ID of the
> > SoC.  Microchip sam-ba has a command 'readuniqueid' which returns the
> > content of the OTPC Product UID x Register in that case.
> > 
> > (On a different board with a SAMA5D2 we use the Serial Number x Register
> > exposed through the atmel soc driver, which is not present in the
> > SAM9X60 series.)
> > 
> > There is a driver for the OTPC of the SAMA7G5 and after comparing
> > register layouts it seems that one is almost identical to the one used
> > by SAM9X60.  So I thought just adapting the driver for SAM9X60 should be
> > easy.  (At least as a start, the driver has no support for that UID
> > register, but I suppose it would be the right place to implement it.)
> > 
> > However it does not work.  I used the patch attached with
> > additional debug messages on a SAM9X60-Curiosity board.  (That patch is
> > not meant for inclusion, just for showing what I've tried.)
> > 
> > On probe the function mchp_otpc_init_packets_list() returns with
> > ETIMEDOUT, which it can only do if mchp_otpc_prepare_read() returns with
> > timeout and that can only happen if read_poll_timeout() times out on
> > reading the Status Register.  Poking that register with `devmem
> > 0xeff0000c 32` gives 0x00000040 which means "A packet read is on-going".
> 
> 
> Would it be possible that the OTP memory is not properly initialized and
> the algorithm to initialized the packet list to confuse the hardware?
> 
> I see in the datasheet the following: "The initial value of the OTP memory
> is ‘0’ but the memory may contain some “defective” bits already set to the
> value ‘1’."

I think this might be possible?  SAM-BA also stumbles here, but the
SoC is like shipped by the vendor, no OTPC writes ever from my side.
When calling this …

    $ sam-ba -p serial -d sam9x60:0:1 -t 5 -a bootconfig -c readcfg:bcp-otp

… I get this on serial debug output:

    Applet 'BootConfig' from SAM-BA Applets Framework 3.8 (v3.8).
    -E- Cannot read Boot Config Packet.
    -E- Invalid parameter for read config: index 0

Question is: how should the driver behave in this case?  Fail like it
does now?  Or load in some kind of safe state with "empty" nvmem?
This is especially interesting with regard to a new question below.

> Otherwise, from the top of my mind I don't have any idea on what might happen.

I have some debug code here, and digging deeper into this currently to
see what's really happening.  While at it, a new question came up:

There's this OTP memory which the driver tries to expose as NVMEM.
However what I really want to do is getting access to the OTPC Product
UID x Registers, which are not OTP memory but plain registers inside
of the address space of the OTPC here.  Should this be exposed as a
second nvmem device then, or handled by a different driver?  How would
accessing the same register space from different drivers be handled
then?

Greets
Alex

> 
> Thank you,
> Claudiu Beznea
> 
> > 
> > Kinda stuck here.  Any ideas?
> > 
> > Greets and have a nice weekend everyone
> > Alex
> > 
> > Alexander Dahl (1):
> >   nvmem: microchip-otpc: Add support for SAM9X60
> > 
> >  .../dts/microchip/at91-sam9x60_curiosity.dts     |  4 ++++
> >  arch/arm/boot/dts/microchip/sam9x60.dtsi         |  7 +++++++
> >  drivers/nvmem/microchip-otpc.c                   | 16 +++++++++++++---
> >  3 files changed, 24 insertions(+), 3 deletions(-)
> > 
> > 
> > base-commit: fec50db7033ea478773b159e0e2efb135270e3b7
> 
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