[PATCH v6 0/4] nvmem: migrate to const void * in reg_write

[Link Mauve]

Oops, I forgot to carry the tag I got in v5…

Here it is:
Reviewed-by: Andy Shevchenko <andriy.shevchenko at intel.com>

On Sun, Sep 20, 2026 at 01:09:53PM +0200, Link Mauve wrote:
> This callback used to take a mutable void * for no reason, which causes
> the compiler to be unaware that the val buffer should never be modified
> by the callback.
> 
> This was found while drafting the nvmem-provider Rust abstraction.
> 
> Thanks to the guidance of Andy Shevchenko, this now introduces a new
> callback and deprecates the existing one, with the goal of renaming the
> new one into the old one once no user remains in the kernel.
> 
> Changes since v5:
> - Link to v5:
>   https://lore.kernel.org/rust-for-linux/20260804135940.2378737-1-linkmauve@linkmauve.fr/T/
> - Add a dev_warn() when registering a nvmem driver with a deprecated
>   reg_write callback.
> - Add a fourth patch enabling COMPILE_TEST on three more nvmem drivers,
>   which forgot to depend on that config.
> - Remove a few unneeded (void *) and (const void *) casts in core.c.
> 
> Changes since v4:
> - Link to v4:
>   https://lore.kernel.org/rust-for-linux/20260726131724.15299-1-linkmauve@linkmauve.fr/T/
> - Rebase on top of linux-next 20260803, the previous series didn’t apply
>   any more due to changes in core.c.
> - Also convert the at24, at25, eeprom_93xx46 and m24lr drivers to the
>   new reg_write_const callback, these were missed because they got moved
>   to the nvmem directory in linux-next between v3 and v4.
> 
> Changes since v3:
> - Link to v3:
>   https://lore.kernel.org/rust-for-linux/20260716142415.28718-1-linkmauve@linkmauve.fr/T/
> - Drop Apple SPMI patch, which had already been independently included
>   in linux-next as 7089170e1df160f5f8fb395bc5aa2e2697b4e896.
> - Reword the cover letter’s subject.
> - Reorder the meson firmware patch before the other ones, so that every
>   commit is always working correctly.
> 
> Changes since v2:
> - Link to v2:
>   https://lore.kernel.org/rust-for-linux/aljAqBNVXV1aVJqx@luna/T/
> - Rebase on top of linux-next/master.
> - Fix logic error which made all devices read-only.
> - Remove a blanket cast of function pointers to void * in
>   apple-spmi-nvmem (patch 3).
> - Also fix constness of write buffer in firmware: meson, which is used
>   exclusively by meson-efuse (patch 4).
> - Re-review all changes to make sure the passed types are more correct
>   than they were before.
> - Actually test with COMPILE_TEST, which I forgot to enable before…
> 
> Changes since v1:
> - Link to v1:
>   https://lore.kernel.org/rust-for-linux/20260715175229.24672-1-linkmauve@linkmauve.fr/
> - Removed all changes to other subsystems than nvmem.
> - Added a new reg_write_const callback instead of changing the exisitng
>   reg_write.
> - Deprecated the existing reg_write callback, it will get removed once
>   all users in the kernel will be done migrating to the new one.
> 
> Link Mauve (4):
>   firmware: meson: pass a const buffer to meson_sm_call_write()
>   nvmem: core: deprecate reg_write callback with reg_write_const
>   nvmem: make all reg_write callbacks take const void *
>   nvmem: enable COMPILE_TEST for more drivers
> 
>  drivers/firmware/meson/meson_sm.c       |  2 +-
>  drivers/nvmem/Kconfig                   |  6 +++---
>  drivers/nvmem/apple-spmi-nvmem.c        |  4 ++--
>  drivers/nvmem/at24.c                    |  6 +++---
>  drivers/nvmem/at25.c                    |  4 ++--
>  drivers/nvmem/bcm-ocotp.c               |  8 ++++----
>  drivers/nvmem/core.c                    | 26 ++++++++++++++++---------
>  drivers/nvmem/eeprom_93xx46.c           |  6 +++---
>  drivers/nvmem/imx-ocotp-scu.c           |  6 +++---
>  drivers/nvmem/imx-ocotp.c               |  6 +++---
>  drivers/nvmem/internals.h               |  1 +
>  drivers/nvmem/lan9662-otpc.c            |  6 +++---
>  drivers/nvmem/lpc18xx_eeprom.c          |  6 +++---
>  drivers/nvmem/m24lr.c                   |  4 ++--
>  drivers/nvmem/max77759-nvmem.c          |  4 ++--
>  drivers/nvmem/meson-efuse.c             |  8 ++++----
>  drivers/nvmem/qcom-spmi-sdam.c          |  6 +++---
>  drivers/nvmem/qfprom.c                  |  6 +++---
>  drivers/nvmem/rave-sp-eeprom.c          |  6 +++---
>  drivers/nvmem/snvs_lpgpr.c              |  4 ++--
>  drivers/nvmem/sprd-efuse.c              |  6 +++---
>  drivers/nvmem/stm32-bsec-optee-ta.c     |  2 +-
>  drivers/nvmem/stm32-bsec-optee-ta.h     |  4 ++--
>  drivers/nvmem/stm32-romem.c             | 10 +++++-----
>  drivers/nvmem/zynqmp_nvmem.c            |  6 +++---
>  include/linux/firmware/meson/meson_sm.h |  2 +-
>  include/linux/nvmem-provider.h          |  6 +++++-
>  27 files changed, 87 insertions(+), 74 deletions(-)
> 
> 
> base-commit: 3f2425f5b5bbbdd991ca9cdfd5502e68d8895998
> -- 
> 2.55.0
> 

-- 
Link Mauve