Re: [PATCH v5 00/21] nvmem: core: introduce NVMEM layouts

[Alexander Stein]

Am Dienstag, 3. Januar 2023, 16:51:31 CET schrieb Srinivas Kandagatla:
> Hi Miquel,
> 
> On 03/01/2023 15:39, Miquel Raynal wrote:
> > Hi Srinivas,
> > 
> > michael@xxxxxxxx wrote on Tue,  6 Dec 2022 21:07:19 +0100:
> >> This is now the third attempt to fetch the MAC addresses from the VPD
> >> for the Kontron sl28 boards. Previous discussions can be found here:
> >> https://lore.kernel.org/lkml/20211228142549.1275412-1-michael@xxxxxxxx/
> >> 
> >> 
> >> NVMEM cells are typically added by board code or by the devicetree. But
> >> as the cells get more complex, there is (valid) push back from the
> >> devicetree maintainers to not put that handling in the devicetree.
> >> 
> >> Therefore, introduce NVMEM layouts. They operate on the NVMEM device and
> >> can add cells during runtime. That way it is possible to add more complex
> >> cells than it is possible right now with the offset/length/bits
> >> description in the device tree. For example, you can have post processing
> >> for individual cells (think of endian swapping, or ethernet offset
> >> handling).
> >> 
> >> The imx-ocotp driver is the only user of the global post processing hook,
> >> convert it to nvmem layouts and drop the global post pocessing hook.
> >> 
> >> For now, the layouts are selected by the device tree. But the idea is
> >> that also board files or other drivers could set a layout. Although no
> >> code for that exists yet.
> >> 
> >> Thanks to Miquel, the device tree bindings are already approved and
> >> merged.
> >> 
> >> NVMEM layouts as modules?
> >> While possible in principle, it doesn't make any sense because the NVMEM
> >> core can't be compiled as a module. The layouts needs to be available at
> >> probe time. (That is also the reason why they get registered with
> >> subsys_initcall().) So if the NVMEM core would be a module, the layouts
> >> could be modules, too.
> > 
> > I believe this series still applies even though -rc1 (and -rc2) are out
> > now, may we know if you consider merging it anytime soon or if there
> > are still discrepancies in the implementation you would like to
> > discuss? Otherwise I would really like to see this laying in -next a
> > few weeks before being sent out to Linus, just in case.
> 
> Thanks for the work!
> 
> Lets get some testing in -next.

This causes the following errors on existing boards (imx8mq-tqma8mq-
mba8mx.dtb):
root@tqma8-common:~# uname -r
6.2.0-rc2-next-20230105

> OF: /soc@0: could not get #nvmem-cell-cells for /soc@0/bus@30000000/
efuse@30350000/soc-uid@4
> OF: /soc@0/bus@30800000/ethernet@30be0000: could not get #nvmem-cell-cells 
for /soc@0/bus@30000000/efuse@30350000/mac-address@90

These are caused because '#nvmem-cell-cells = <0>;' is not explicitly set in 
DT.

> TI DP83867 30be0000.ethernet-1:0e: error -EINVAL: failed to get nvmem cell 
io_impedance_ctrl
> TI DP83867: probe of 30be0000.ethernet-1:0e failed with error -22

These are caused because of_nvmem_cell_get() now returns -EINVAL instead of -
ENODEV if the requested nvmem cell is not available.

Best regards,
Alexander