netdev - RE: [PATCH v4 2/3] net: ethernet: renesas: Add Ethernet Switch driver

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Date:   Tue, 25 Oct 2022 04:39:44 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        kernel test robot <lkp@...el.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH v4 2/3] net: ethernet: renesas: Add Ethernet Switch driver

Hi Geert-san,

> From: Geert Uytterhoeven, Sent: Tuesday, October 25, 2022 12:28 AM
> To: kernel test robot <lkp@...el.com>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>; davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> pabeni@...hat.com; robh+dt@...nel.org; krzysztof.kozlowski+dt@...aro.org; kbuild-all@...ts.01.org;
> netdev@...r.kernel.org; devicetree@...r.kernel.org; linux-renesas-soc@...r.kernel.org
> Subject: Re: [PATCH v4 2/3] net: ethernet: renesas: Add Ethernet Switch driver
> 
> On Wed, Oct 19, 2022 at 1:17 PM kernel test robot <lkp@...el.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
> >
<snip>
> >         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@...el.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.

I got it. I'll fix this by a cast to "u64".

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

Yes, all rswitch_xxx_desc just extend struct rswitch_desc.
So, I'll modify this function like below:
---
/* All struct rswitch_xxx_desc just extend struct rswitch_desc, so that
 * we can use rswitch_desc_get_dptr() for them.
 */
static dma_addr_t rswitch_desc_get_dptr(void *_desc)
{
        struct rswitch_desc *desc = _desc;

        return __le32_to_cpu(desc->dptrl) | (u64)(desc->dptrh) << 32;
}
---

Best regards,
Yoshihiro Shimoda