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Message-ID: <20240701-nuttiness-backlit-60ccfea75b56@thorsis.com>
Date: Mon, 1 Jul 2024 09:40:56 +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,
Cyrille Pitchen <cyrille.pitchen@...rochip.com>
Subject: Re: [RFC PATCH 0/1] Timeout error with Microchip OTPC driver on
SAM9X60
Hei hei,
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’."
Meanwhile we looked deeper into this driver. I just drop here what we
found so far, because it's vacation time, and this will probably not
be picked up again this month because vacation etc. I wanna get it
out of my head for now. ;-)
Note: most of this should also apply to sama7g5, from comparing data
sheets the OTPC is the same.
1. the call to read_poll_timeout() most probably has its sleep and
timeout paramaters swapped.
2. the read access to OTPC_CR register is not necessary, the datasheet
says the register is "write only". It may even trigger an interrupt
for reading a write only register. Furthermore the WPCTEN bit in the
OTPC Write Protection Mode register (OTPC_WPMR) is not checked before
accessing OTPC_CR as suggested by the datasheet.
3. the errata sheet for the SAM9X60 SoC (DS80000846) has a section on
the OTPC which recommends a fixup before the first write operation,
with code example:
https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ProductDocuments/Errata/SAM9X60-Device-Silicon-Errata-and-Data-Sheet-Clarif-DS80000846.pdf
The same thing is implemented in 'atmel-software-package' which has
(at least had in the past) the code for the binary applets used in the
'sam-ba' tool:
https://github.com/atmelcorp/atmel-software-package/blame/master/drivers/nvm/otp/otpc.c#L86
I bet this fixup should be implemented in this driver here as well?
So far for now.
Greets
Alex
>
> Otherwise, from the top of my mind I don't have any idea on what might happen.
>
> 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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