netdev - Re: [PATCH] net: ethernet: mediatek: Fix overlapping capability bits.

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Date:   Mon, 1 Jul 2019 08:57:29 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     René van Dorst <opensource@...rst.com>
Cc:     sean.wang@...iatek.com, Florian Fainelli <f.fainelli@...il.com>,
        linux@...linux.org.uk, David Miller <davem@...emloft.net>,
        matthias.bgg@...il.com, andrew@...n.ch, vivien.didelot@...il.com,
        frank-w@...lic-files.de,
        Network Development <netdev@...r.kernel.org>,
        linux-mediatek@...ts.infradead.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH] net: ethernet: mediatek: Fix overlapping capability bits.

On Mon, Jul 1, 2019 at 8:44 AM René van Dorst <opensource@...rst.com> wrote:
>
> Quoting Willem de Bruijn <willemdebruijn.kernel@...il.com>:
>
> > On Sat, Jun 29, 2019 at 8:24 AM René van Dorst <opensource@...rst.com> wrote:
> >>
> >> Both MTK_TRGMII_MT7621_CLK and MTK_PATH_BIT are defined as bit 10.
> >>
> >> This causes issues on non-MT7621 devices which has the
> >> MTK_PATH_BIT(MTK_ETH_PATH_GMAC1_RGMII) capability set.
> >> The wrong TRGMII setup code is executed.
> >>
> >> Moving the MTK_PATH_BIT to bit 11 fixes the issue.
> >>
> >> Fixes: 8efaa653a8a5 ("net: ethernet: mediatek: Add MT7621 TRGMII mode
> >> support")
> >> Signed-off-by: René van Dorst <opensource@...rst.com>
> >
> > This targets net? Please mark networking patches [PATCH net] or [PATCH
> > net-next].
>
> Hi Willem,
>
> Thanks for you input.
>
> This patch was for net-next.
>
> >
> >> ---
> >>  drivers/net/ethernet/mediatek/mtk_eth_soc.h | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> >> b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> >> index 876ce6798709..2cb8a915731c 100644
> >> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> >> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> >> @@ -626,7 +626,7 @@ enum mtk_eth_path {
> >>  #define MTK_TRGMII_MT7621_CLK          BIT(10)
> >>
> >>  /* Supported path present on SoCs */
> >> -#define MTK_PATH_BIT(x)         BIT((x) + 10)
> >>
> >> +#define MTK_PATH_BIT(x)         BIT((x) + 11)
> >>
> >
> > To avoid this happening again, perhaps make the reserved range more explicit?
> >
> > For instance
> >
> > #define MTK_FIXED_BIT_LAST 10
> > #define MTK_TRGMII_MT7621_CLK  BIT(MTK_FIXED_BIT_LAST)
> >
> > #define MTK_PATH_BIT_FIRST  (MTK_FIXED_BIT_LAST + 1)
> > #define MTK_PATH_BIT_LAST (MTK_FIXED_BIT_LAST + 7)
> > #define MTK_MUX_BIT_FIRST (MTK_PATH_BIT_LAST + 1)
> >
> > Though I imagine there are cleaner approaches. Perhaps define all
> > fields as enum instead of just mtk_eth_mux and mtk_eth_path. Then
> > there can be no accidental collision.
>
> You mean in a similar way as done in the ethtool.h [0]?
>
> Use a enum to define the unique bits.
>
> enum mtk_bits {
>         MTK_RGMII_BIT = 0,
>         MTK_SGMII_BIT,
>         MTK_TRGMII_BIT,
>         AND SO ON ....
> };
>
> Also move the mtk_eth_mux and mtk_eth_path in to this enum.

That's the key part: they are all part of the same namespace and these
enums are not used anywhere else, so a single enum will avoid
accidentally namespace collisions.

> Then use defines to convert bits to values.
>
> #define MTK_RGMII  BIT(MTK_RGMII_BIT)
> #define MTK_TRGMII BIT(MTK_TRGMII_BIT)
>
> Replace the MTK_PATH_BIT and MTK_PATH_BIT macro with BIT()
>
> Is this what you had in mind?

Great find. Exactly, but I did not find such a clear example.

>
> Greats,
>
> René
>
> [0]:
> https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/ethtool.h#L1402
>
>
>