Subject: Re: Adding OTP-only device to MTD or CHAR subsystem?
To: Arnd Bergmann <arnd@arndb.de>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Maxime Ripard <maxime.ripard@free-electrons.com>
References: <5681C3E4.4090506@broadcom.com> <3668194.4jROlECW6L@wuerfel>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Brian Norris <computersforpeace@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>
From: Scott Branden <sbranden@broadcom.com>
Message-ID: <5681D4B0.3040804@broadcom.com>
Date: Mon, 28 Dec 2015 16:32:48 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.4.0
MIME-Version: 1.0
In-Reply-To: <3668194.4jROlECW6L@wuerfel>
Content-Type: text/plain; charset="windows-1252"; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2079
Lines: 47

+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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/