Re: [PATCH v1 v1 3/4] rust: fb: add framebuffer driver support

[kernel test robot <lkp@intel.com>]

Hi pengfuyuan,

kernel test robot noticed the following build errors:

[auto build test ERROR on rust/rust-next]
[also build test ERROR on driver-core/driver-core-linus linus/master v6.19-rc7]
[cannot apply to driver-core/driver-core-testing driver-core/driver-core-next next-20260123]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/pengfuyuan/rust-io-mem-add-ioremap_wc-support/20260126-162117
base:   https://github.com/Rust-for-Linux/linux rust-next
patch link:    https://lore.kernel.org/r/20260126081744.781392-4-pengfuyuan%40kylinos.cn
patch subject: [PATCH v1 v1 3/4] rust: fb: add framebuffer driver support
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20260127/202601270630.FHzCSbVv-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260127/202601270630.FHzCSbVv-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601270630.FHzCSbVv-lkp@intel.com/

All errors (new ones prefixed by >>):

>> error[E0308]: mismatched types
   --> rust/kernel/fb/device.rs:307:23
   |
   307 |         fb_read: Some(Self::read_callback),
   |                  ---- ^^^^^^^^^^^^^^^^^^^ expected fn pointer, found fn item
   |                  |
   |                  arguments to this enum variant are incorrect
   |
   = note: expected fn pointer `unsafe extern "C" fn(_, *mut u8, _, _) -> _`
   found fn item `extern "C" fn(_, *mut i8, _, _) -> _ {fb::device::Device::<T>::read_callback}`
   help: the type constructed contains `extern "C" fn(*mut fb_info, *mut i8, usize, *mut i64) -> isize {fb::device::Device::<T>::read_callback}` due to the type of the argument passed
   --> rust/kernel/fb/device.rs:307:18
   |
   307 |         fb_read: Some(Self::read_callback),
   |                  ^^^^^-------------------^
   |                       |
   |                       this argument influences the type of `Some`
   note: tuple variant defined here
   --> /opt/cross/rustc-1.88.0-bindgen-0.72.1/rustup/toolchains/1.88.0-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:597:5
   |
   597 |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
   |     ^^^^
--
>> error[E0308]: mismatched types
   --> rust/kernel/fb/device.rs:308:24
   |
   308 |         fb_write: Some(Self::write_callback),
   |                   ---- ^^^^^^^^^^^^^^^^^^^^ expected fn pointer, found fn item
   |                   |
   |                   arguments to this enum variant are incorrect
   |
   = note: expected fn pointer `unsafe extern "C" fn(_, *const u8, _, _) -> _`
   found fn item `extern "C" fn(_, *const i8, _, _) -> _ {fb::device::Device::<T>::write_callback}`
   help: the type constructed contains `extern "C" fn(*mut fb_info, *const i8, usize, *mut i64) -> isize {fb::device::Device::<T>::write_callback}` due to the type of the argument passed
   --> rust/kernel/fb/device.rs:308:19
   |
   308 |         fb_write: Some(Self::write_callback),
   |                   ^^^^^--------------------^
   |                        |
   |                        this argument influences the type of `Some`
   note: tuple variant defined here
   --> /opt/cross/rustc-1.88.0-bindgen-0.72.1/rustup/toolchains/1.88.0-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:597:5
   |
   597 |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
   |     ^^^^
--
>> error[E0308]: mismatched types
   --> rust/kernel/fb/io.rs:32:13
   |
   30     |         bindings::fb_io_read(
   |         -------------------- arguments to this function are incorrect
   31     |             device.as_raw(),
   32     |             buf.as_mut_ptr() as *mut core::ffi::c_char,
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*mut u8`, found `*mut i8`
   |
   = note: expected raw pointer `*mut u8`
   found raw pointer `*mut i8`
   note: function defined here
   --> rust/bindings/bindings_generated.rs:123562:12
   |
   123562 |     pub fn fb_io_read(
   |            ^^^^^^^^^^
--
>> error[E0308]: mismatched types
   --> rust/kernel/fb/io.rs:58:13
   |
   56     |         bindings::fb_io_write(
   |         --------------------- arguments to this function are incorrect
   57     |             device.as_raw(),
   58     |             buf.as_ptr() as *const core::ffi::c_char,
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `*const u8`, found `*const i8`
   |
   = note: expected raw pointer `*const u8`
   found raw pointer `*const i8`
   note: function defined here
   --> rust/bindings/bindings_generated.rs:123570:12
   |
   123570 |     pub fn fb_io_write(
   |            ^^^^^^^^^^^

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