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Message-ID: <CAA9_cmcfQ-cYHtQR63ENtygZwaz6OPFsXbmQEZBZesyJqC=qsw@mail.gmail.com>
Date: Fri, 29 May 2015 14:44:33 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Sascha Hauer <s.hauer@...gutronix.de>, sboyd@...eaurora.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
Rob Herring <robh+dt@...nel.org>,
Mark Brown <broonie@...nel.org>,
Kumar Gala <galak@...eaurora.org>,
Matthew Porter <mporter@...sulko.com>,
Maxime Ripard <maxime.ripard@...e-electrons.com>,
linux-api@...r.kernel.org,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 00/11] Add simple NVMEM Framework via regmap.
On Fri, May 29, 2015 at 12:09 AM, Srinivas Kandagatla
<srinivas.kandagatla@...aro.org> wrote:
>
>
> On 29/05/15 02:20, Dan Williams wrote:
>>
>> On Thu, May 21, 2015 at 9:42 AM, Srinivas Kandagatla
>> <srinivas.kandagatla@...aro.org> wrote:
>>>
>>> Thankyou all for providing inputs and comments on previous versions of
>>> this patchset.
>>> Here is the v5 of the patchset addressing all the issues raised as
>>> part of previous versions review.
>>>
>>> This patchset adds a new simple NVMEM framework to kernel.
>>>
>>> Up until now, NVMEM drivers were stored in drivers/misc, where they all
>>> had to
>>> duplicate pretty much the same code to register a sysfs file, allow
>>> in-kernel
>>> users to access the content of the devices they were driving, etc.
>>>
>>> This was also a problem as far as other in-kernel users were involved,
>>> since
>>> the solutions used were pretty much different from on driver to another,
>>> there
>>> was a rather big abstraction leak.
>>>
>>> Introduction of this framework aims at solving this. It also introduces
>>> DT
>>> representation for consumer devices to go get the data they require (MAC
>>> Addresses, SoC/Revision ID, part numbers, and so on) from the NVMEMs.
>>>
>>> After learning few things about QCOM qfprom and other eeprom/efuses,
>>> which
>>> has packed fields at bit level. Which makes it important to add support
>>> to
>>> such memories. This version adds support to this type of non volatile
>>> memories by adding support to bit level nvmem-cells.
>>>
>>> Having regmap interface to this framework would give much better
>>> abstraction for nvmems on different buses.
>>>
>>> patch 1-2 Introduces two regmap helper functions.
>>> patch 3-6 Introduces the NVMEM framework.
>>> Patch 7 Adds helper functions for nvmems based on mmio.
>>> Patch 8 migrates an existing driver to nvmem framework.
>>> Patch 9-10 Adds Qualcomm specific qfprom driver.
>>> Patch 11 adds entry in MAINTAINERS.
>>>
>>> Its also possible to migrate other nvmem drivers to this framework.
>>>
>>> Providers APIs:
>>> nvmem_register/unregister();
>>>
>>> Consumers APIs:
>>> Cell based apis for both DT/Non-DT:
>>> nvmem_cell_get()/nvmem_cell_put();
>>> nvmem_cell_read()/nvmem_cell_write();
>>>
>>> Raw byte access apis for both DT/non-DT.
>>> nvmem_device_get()/nvmem_device_put()
>>> nvmem_device_read()/nvmem_device_write();
>>> nvmem_device_cell_read()/nvmem_device_cell_write();
>>>
>>> Device Tree:
>>>
>>> /* Provider */
>>> qfprom: qfprom@...00000 {
>>> ...
>>>
>>> /* Data cells */
>>> tsens_calibration: calib@404 {
>>> reg = <0x404 0x10>;
>>> };
>>>
>>> tsens_calibration_bckp: calib_bckp@504 {
>>> reg = <0x504 0x11>;
>>> bit-offset = 6;
>>> nbits = 128;
>>> };
>>>
>>> pvs_version: pvs-version@6 {
>>> reg = <0x6 0x2>
>>> bit-offset = 7;
>>> nbits = 2;
>>> };
>>>
>>> speed_bin: speed-bin@c{
>>> reg = <0xc 0x1>;
>>> bit-offset = 2;
>>> nbits = 3;
>>>
>>> };
>>> ...
>>> };
>>>
>>> userspace interface: binary file in /sys/class/nvmem/*/nvmem
>>>
>>> ex:
>>> hexdump /sys/class/nvmem/qfprom0/nvmem
>>>
>>> 0000000 0000 0000 0000 0000 0000 0000 0000 0000
>>> *
>>> 00000a0 db10 2240 0000 e000 0c00 0c00 0000 0c00
>>> 0000000 0000 0000 0000 0000 0000 0000 0000 0000
>>> ...
>>> *
>>> 0001000
>>>
>>> Changes since v4(https://lkml.org/lkml/2015/3/30/725)
>>> * rename eeprom to nvmem suggested by Matt Porter
>>
>>
>> Apologies for the bikeshed fly-by review, but given we already have
>> NVME and are adding an NVDIMM driver sub-system is s/eeprom/nvmem/ a
>> good idea?
>>
> IMO yes.
>
> I did briefly looked at NVME before renaming the eeprom to nvmem,
> NVME is aimed at defining the command/feature set for PCIe-based SSDs with
> the goals of increased and efficient performance and interoperability.
>
> This patch-set introduces simple nvmem which is applicable for non volatile
> memories like efuses, eeprom, ROM, NVRAM .. etc, which are used in most
> boards/SBC's. Data like calibration table, mac address or opps, are
> generally stored this. This data is required by multiple drivers and
> currently there is no framework in the kernel to address/abstract this,
> resulting in code duplication.
Understood, but don't be surprised when people confuse NVMEM support
(sub to single digit megabyte capacities for firmware) and NVDIMM
support (multiple gigabyte capacities for i/o).
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