linux-kernel - Re: [RFC PATCH v6 2/2] nvmem: Add Vybrid OCOTP and OCROM support

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Date:	Wed, 24 Jun 2015 13:20:56 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	Stefan Wahren <stefan.wahren@...e.com>
Cc:	maitysanchayan@...il.com, srinivas.kandagatla@...aro.org,
	maxime.ripard@...e-electrons.com,
	linux-arm-kernel@...ts.infradead.org, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, shawn.guo@...aro.org, arnd@...db.de
Subject: Re: [RFC PATCH v6 2/2] nvmem: Add Vybrid OCOTP and OCROM support

On 2015-06-24 11:56, Stefan Wahren wrote:
> Hi Sanchayan,
> 
> Am 24.06.2015 um 07:19 schrieb maitysanchayan@...il.com:
>> On 15-06-23 21:31:41, Stefan Wahren wrote:
>>> Hi Sanchayan,
>>>
>>>> Sanchayan Maity <maitysanchayan@...il.com> hat am 23. Juni 2015 um 15:44
>>>> geschrieben:
>>>>
>>>>
>>>> The patch adds support for the On Chip One Time Programmable Peripheral
>>>> (OCOTP) and On Chip ROM (OCROM) support.
>>>>
>>>> On Vybrid OCOTP contain data like SoC ID, MAC address and OCROM has the
>>>> revision ID.
>>>>
>>>> Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>
>>>> ---
>>>> drivers/nvmem/Kconfig | 11 +++++++++
>>>> drivers/nvmem/Makefile | 2 ++
>>>> drivers/nvmem/vf610-ocotp.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
>>>> 3 files changed, 73 insertions(+)
>>>> create mode 100644 drivers/nvmem/vf610-ocotp.c
>>>>
>>>> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
>>>> index 17f1a57..557c1e0 100644
>>>> --- a/drivers/nvmem/Kconfig
>>>> +++ b/drivers/nvmem/Kconfig
>>>> @@ -33,4 +33,15 @@ config NVMEM_SUNXI_SID
>>>> This driver can also be built as a module. If so, the module
>>>> will be called eeprom-sunxi-sid.
>>>>
>>>> +config NVMEM_VF610_OCOTP
>>>> + tristate "VF610 SoCs OCOTP support"
>>>> + depends on SOC_VF610
>>>> + select REGMAP_MMIO
>>> how do you come to the conclusion that Vybrid On-Chip OTP is accessable via
>>> MMIO?
>> Frankly speaking I just changed the naming conventions and followed the qfrom
>> and sunxi sid examples in Srinivas's patches.
>>
>> I just tested it without the "select REGMAP_MMIO" and it works just fine.
>>
>> - Sanchayan.
> 
> sorry for the confusion. My question refers to the whole driver
> implementation not only to the REGMAP_MMIO.
> 
> According to
> 
> Vybrid Reference Manual F-Series
> Document Number: VYBRIDRM
> Rev 7, 06/2014
> 
> 35.5 OCOTP memory map/register definition
> 
> the memory region is organized in control and shadow registers. I'm very
> sceptical that using REGMAP_MMIO is the right way for accessing the OCOTP.
> 
> It possible that it works in your case. But in the case the lock bits
> are set the driver won't work correctly.

The OCOTP represents fuses, starting from 0x400A5400 one can access the
shadowed registers containing the fuses values. The reference manual
also says: "All shadow registers are always readable through the APB bus
except some secret key"

The driver does not need write access. I guess it is fine to use only
reads through regmap...?

--
Stefan
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