From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754077AbcAILNb (ORCPT ); Sat, 9 Jan 2016 06:13:31 -0500 Received: from mail-wm0-f51.google.com ([74.125.82.51]:34948 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753211AbcAILN3 (ORCPT ); Sat, 9 Jan 2016 06:13:29 -0500 Message-ID: <5690EB4D.3080002@linaro.org> Date: Sat, 09 Jan 2016 11:13:17 +0000 From: Srinivas Kandagatla User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Scott Branden , Arnd Bergmann , Maxime Ripard CC: Greg Kroah-Hartman , Brian Norris , "linux-kernel@vger.kernel.org" , "linux-mtd@lists.infradead.org" Subject: Re: Adding OTP-only device to MTD or CHAR subsystem? References: <5681C3E4.4090506@broadcom.com> <3668194.4jROlECW6L@wuerfel> <5681D4B0.3040804@broadcom.com> In-Reply-To: <5681D4B0.3040804@broadcom.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Scott, Sorry for long delay in replying.. :-) On 29/12/15 00:32, Scott Branden wrote: > +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? NVMEM was started to be simple interface based on regmap, As of today we did not have any users which wanted lock feature, but Am open for more discussion on this if we want to get this feature via nvmem. Any ideas and patches are welcome. Few ideas from my side though, From Kernel side: introduce nvmem_lock()/nvmem_unlock() apis which would set the ranges as required, and the providers can use regmap callbacks writeable_reg()/readable_reg() in regmap configs to enforce the lock range From userspace side, As of today nvmem only provides an binary file interface, which we could probably extend to device based and provide userspace abi. Lets continue discussion !! --srini >> >> Arnd >> > Regards, > Scott