Re: [PATCH v5 00/11] Add simple NVMEM Framework via regmap.

[Dan Williams]

On Fri, May 29, 2015 at 12:09 AM, Srinivas Kandagatla
<srinivas.kandagatla@xxxxxxxxxx> wrote:
>
>
> On 29/05/15 02:20, Dan Williams wrote:
>>
>> On Thu, May 21, 2015 at 9:42 AM, Srinivas Kandagatla
>> <srinivas.kandagatla@xxxxxxxxxx> 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@00700000 {
>>>                  ...
>>>
>>>                  /* 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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