Re: [PATCH] PCI: Annotate pci_cache_line_size variables as __ro_after_init

[Bjorn Helgaas <helgaas@kernel.org>]

On Sat, Apr 13, 2024 at 11:05:52PM +0200, Heiner Kallweit wrote:
> Annotate both variables as __ro_after_init, enforcing that they can't
> be changed after the init phase.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  drivers/pci/pci.c   | 4 ++--
>  include/linux/pci.h | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 5f8edba78..e7ac4474b 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -142,8 +142,8 @@ enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;
>   * the dfl or actual value as it sees fit.  Don't forget this is
>   * measured in 32-bit words, not bytes.
>   */
> -u8 pci_dfl_cache_line_size = L1_CACHE_BYTES >> 2;
> -u8 pci_cache_line_size;
> +u8 pci_dfl_cache_line_size __ro_after_init = L1_CACHE_BYTES >> 2;
> +u8 pci_cache_line_size __ro_after_init;
>  
>  /*
>   * If we set up a device for bus mastering, we need to check the latency
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 69b10f2fb..cf63be0c9 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2334,8 +2334,8 @@ extern int pci_pci_problems;
>  
>  extern unsigned long pci_cardbus_io_size;
>  extern unsigned long pci_cardbus_mem_size;
> -extern u8 pci_dfl_cache_line_size;
> -extern u8 pci_cache_line_size;
> +extern u8 pci_dfl_cache_line_size __ro_after_init;
> +extern u8 pci_cache_line_size __ro_after_init;

Is __ro_after_init required on the declaration, too?  I see a few uses
in .h files, but not very many, and I would think it would be a linker
thing that applies to the definition, where space is allocated.

>  /* Architecture-specific versions may override these (weak) */
>  void pcibios_disable_device(struct pci_dev *dev);
> -- 
> 2.44.0
>