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Adding OTP-only device to MTD or CHAR subsystem?

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  Adding OTP-only device to MTD or CHAR subsystem? Scott Branden <sbranden@broadcom.com> - 2015-12-29 00:30 +0100
    Re: Adding OTP-only device to MTD or CHAR subsystem? Arnd Bergmann <arnd@arndb.de> - 2015-12-29 00:40 +0100
      Re: Adding OTP-only device to MTD or CHAR subsystem? Scott Branden <sbranden@broadcom.com> - 2015-12-29 01:40 +0100

#1298790 — Adding OTP-only device to MTD or CHAR subsystem?

Greg/Brian/Arnd,

We have OTP device drivers for accessing OTP memory in our SoCs.

I looking for the right place and model to place such OTP device drivers.

1) Should we follow the bfin-otp model in drivers/char?  This doesn't 
seem like the right place to put it although following the bfin example 
is quite simple to implement.  We actually had a custom set of Ioctl's 
that I changed to use the standard file access model used by the bfin 
driver.  But a custom util is still needed to issue an OTPLOCK command. 
  I'm guess mtd-utils has such abilities (or should).

2) Instead, should we start adding OTP-only drivers into the MTD 
subsystem?  Onenand and CFI based MTD devices already have OTP 
programmable regions.  If we created a new OTP device type in the MTD 
subsystem this looks like a good thing to do.  mtd-utils could/should be 
used to access the OTP device then along with standard fileio operations.

3) Or some other suggestion of where to place OTP device drivers?

Regards,
  Scott
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#1298796

On Monday 28 December 2015 15:21:08 Scott Branden wrote:
> Greg/Brian/Arnd,
> 
> We have OTP device drivers for accessing OTP memory in our SoCs.
> 
> I looking for the right place and model to place such OTP device drivers.
> 
> 1) Should we follow the bfin-otp model in drivers/char?  This doesn't 
> seem like the right place to put it although following the bfin example 
> is quite simple to implement.  We actually had a custom set of Ioctl's 
> that I changed to use the standard file access model used by the bfin 
> driver.  But a custom util is still needed to issue an OTPLOCK command. 
>   I'm guess mtd-utils has such abilities (or should).
> 
> 2) Instead, should we start adding OTP-only drivers into the MTD 
> subsystem?  Onenand and CFI based MTD devices already have OTP 
> programmable regions.  If we created a new OTP device type in the MTD 
> subsystem this looks like a good thing to do.  mtd-utils could/should be 
> used to access the OTP device then along with standard fileio operations.
> 
> 3) Or some other suggestion of where to place OTP device drivers?

I think drivers/nvmem is now the right place for this.

	Arnd
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#1298815

+Srinivas/Maxime

On 15-12-28 03:38 PM, Arnd Bergmann wrote:
> On Monday 28 December 2015 15:21:08 Scott Branden wrote:
>> Greg/Brian/Arnd,
>>
>> We have OTP device drivers for accessing OTP memory in our SoCs.
>>
>> I looking for the right place and model to place such OTP device drivers.
>>
>> 1) Should we follow the bfin-otp model in drivers/char?  This doesn't
>> seem like the right place to put it although following the bfin example
>> is quite simple to implement.  We actually had a custom set of Ioctl's
>> that I changed to use the standard file access model used by the bfin
>> driver.  But a custom util is still needed to issue an OTPLOCK command.
>>    I'm guess mtd-utils has such abilities (or should).
>>
>> 2) Instead, should we start adding OTP-only drivers into the MTD
>> subsystem?  Onenand and CFI based MTD devices already have OTP
>> programmable regions.  If we created a new OTP device type in the MTD
>> subsystem this looks like a good thing to do.  mtd-utils could/should be
>> used to access the OTP device then along with standard fileio operations.
>>
>> 3) Or some other suggestion of where to place OTP device drivers?
>
> I think drivers/nvmem is now the right place for this.
Thanks for the pointer Arnd.  Too bad an extension wasn't added in MTD 
but at least there is some sort of a model in place now.  The mtd-abi.h 
would have been a good thing to use for OTPLOCK as well as the remainder 
of the functionality in MTD OTP.  The mapping of nvmem to properties to 
user settings seems like a useful feature though.

Hi Srinivas/Maxime,
The nvmem drivers don't seem to support row unlocking of OTP.  Having 
raw write access to the OTP is not a desirable feature.  Are there plans 
in place to add any additional functionality to the nvm driver model 
right now?
>
> 	Arnd
>
Regards,
  Scott
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