Re: [PATCH] alpha: Use generic <asm-generic/io.h>

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Aug 18, 2022 at 11:20:59AM +0200, Linus Walleij wrote:
> This enables the alpha to use <asm-generic/io.h> to fill in the
> missing (undefined) I/O accessor functions.
> 
> This is needed if Alpha ever wants to uses CONFIG_REGMAP_MMIO
> which has been patches to use accelerated _noinc accessors
> such as readsq/writesq that Alpha, while being a 64bit platform,
> as of now not yet provide. readq/writeq is however provided
> so the machine can do 64bit I/O.
> 
> This comes with the requirement that everything the architecture
> already provides needs to be defined, rather than just being,
> say, static inline functions.
> 
> Bite the bullet and just provide the definitions and make it work.
> 
> Alternative approaches:
> 
> - Implement proper readsq/writesq inline accessors for alpha
> - Rewrite the whole world of io.h to use something like __weak
>   instead of relying on defines
> - Leave regmap MMIO broken on Alpha because none of its drivers
>   use it
> - Make regmap MMIO depend of !ARCH_ALPHA
> 
> The latter seems a bit over the top. First option to implement
> readsq/writesq seems possible but I cannot test it (no hardware)
> so using the generic fallbacks seems like a better idea, also in
> general that will provide future defaults for accelerated defines.
> 
> Leaving regmap MMIO broken or disabling it for Alpha feels bad
> because it breaks compiler coverage.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/linux-mm/202208181447.G9FLcMkI-lkp@intel.com/
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> Cc: Matt Turner <mattst88@gmail.com>
> Cc: linux-arch@vger.kernel.org
> Cc: linux-alpha@vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

This patch results in the following build errors when trying to build
alpha:allmodconfig.

ERROR: modpost: "ioread64" [drivers/pci/switch/switchtec.ko] undefined!
ERROR: modpost: "ioread64" [drivers/net/ethernet/freescale/enetc/fsl-enetc.ko] undefined!
ERROR: modpost: "ioread64" [drivers/net/ethernet/freescale/enetc/fsl-enetc-vf.ko] undefined!
ERROR: modpost: "iowrite64" [drivers/net/ethernet/xilinx/xilinx_emac.ko] undefined!
ERROR: modpost: "iowrite64" [drivers/net/wwan/t7xx/mtk_t7xx.ko] undefined!
ERROR: modpost: "ioread64" [drivers/net/wwan/t7xx/mtk_t7xx.ko] undefined!
ERROR: modpost: "iowrite64" [drivers/firmware/arm_scmi/scmi-module.ko] undefined!
ERROR: modpost: "ioread64" [drivers/firmware/arm_scmi/scmi-module.ko] undefined!
ERROR: modpost: "iowrite64" [drivers/vfio/pci/vfio-pci-core.ko] undefined!
ERROR: modpost: "ioread64" [drivers/ntb/hw/mscc/ntb_hw_switchtec.ko] undefined!

Reverting it doesn't help because that just reintroduces the problem
that was supposed to be fixed by this patch.

Guenter