On Thu Jul 16, 2026 at 3:24 PM BST, 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.
I wouldn't call the series "const-unsoundness fix". There's nothing wrong (in
the sense of UB) in using "void *" for constant data as long as it is not
actually mutated. Yes, it's better to use "const void *", but just call it
"migrate to const void * in reg_write" or something similar.
Best,
Gary
>
> 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):
> nvmem: core: deprecate reg_write callback and add reg_write_const
> nvmem: make all reg_write callbacks take const void *
> nvmem: apple-spmi: improve calling safety with wrapper functions
> firmware: meson: pass a const buffer to meson_sm_call_write()
>
> drivers/firmware/meson/meson_sm.c | 2 +-
> drivers/nvmem/apple-spmi-nvmem.c | 18 ++++++++++++++--
> drivers/nvmem/bcm-ocotp.c | 8 +++----
> drivers/nvmem/core.c | 28 ++++++++++++++-----------
> 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/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 +++++-
> 22 files changed, 87 insertions(+), 64 deletions(-)
>
>
> base-commit: b8809969e1d7a591e0f49dd464a5d04b3cf02ab1