Re: [PATCH v4 2/3] net: ethernet: renesas: Add Ethernet Switch driver

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Wed, Oct 19, 2022 at 1:17 PM kernel test robot <lkp@intel.com> wrote:
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on net-next/master]
> [also build test WARNING on net/master robh/for-next linus/master v6.1-rc1 next-20221019]
> [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/Yoshihiro-Shimoda/net-ethernet-renesas-Add-Ethernet-Switch-driver/20221019-163806
> patch link:    https://lore.kernel.org/r/20221019083518.933070-3-yoshihiro.shimoda.uh%40renesas.com
> patch subject: [PATCH v4 2/3] net: ethernet: renesas: Add Ethernet Switch driver
> config: m68k-allyesconfig
> compiler: m68k-linux-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/f310f8cc37dfb090cfb06ae38530276327569464
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Yoshihiro-Shimoda/net-ethernet-renesas-Add-Ethernet-Switch-driver/20221019-163806
>         git checkout f310f8cc37dfb090cfb06ae38530276327569464
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash drivers/net/
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
>    drivers/net/ethernet/renesas/rswitch.c: In function 'rswitch_ext_desc_get_dptr':
> >> drivers/net/ethernet/renesas/rswitch.c:355:71: warning: left shift count >= width of type [-Wshift-count-overflow]
>      355 |         return __le32_to_cpu(desc->dptrl) | (dma_addr_t)(desc->dptrh) << 32;
>          |                                                                       ^~
>    drivers/net/ethernet/renesas/rswitch.c: In function 'rswitch_ext_ts_desc_get_dptr':
>    drivers/net/ethernet/renesas/rswitch.c:367:71: warning: left shift count >= width of type [-Wshift-count-overflow]
>      367 |         return __le32_to_cpu(desc->dptrl) | (dma_addr_t)(desc->dptrh) << 32;
>          |                                                                       ^~
>
>
> vim +355 drivers/net/ethernet/renesas/rswitch.c
>
>    352
>    353  static dma_addr_t rswitch_ext_desc_get_dptr(struct rswitch_ext_desc *desc)
>    354  {
>  > 355          return __le32_to_cpu(desc->dptrl) | (dma_addr_t)(desc->dptrh) << 32;

A simple fix would be to replace the cast to "dma_addr_t" by a cast to "u64".
A more convoluted fix would be:

    dma_addr_t dma;

    dma = __le32_to_cpu(desc->dptrl);
    if (IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT))
            dma |= (u64)desc->dptrh << 32;
    return dma;

Looking at the gcc compiler output, the both cases are optimized to the
exact same code, for both arm32 and arm64, so I'd go for the simple fix.

BTW, if struct rswitch_ext_desc would just extend struct rswitch_desc,
you could use rswitch_ext_desc_get_dptr() for both.

>    356  }
>    357

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds