linux-kernel - Re: Adding OTP-only device to MTD or CHAR subsystem?

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Date:	Mon, 28 Dec 2015 16:32:48 -0800
From:	Scott Branden <sbranden@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Brian Norris <computersforpeace@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
Subject: Re: Adding OTP-only device to MTD or CHAR subsystem?

+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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