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

[Srinivas Kandagatla]

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.


--srini
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