netdev - Re: [PATCH net-next] rswitch: Add PM ops

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Message-ID: <CAMuHMdUNrdr8YTQBxzX=7=W+SBtK-uH6CjjUgR9VRj3CpKFh1g@mail.gmail.com>
Date: Fri, 13 Oct 2023 11:19:15 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc: "s.shtylyov@....ru" <s.shtylyov@....ru>, "davem@...emloft.net" <davem@...emloft.net>, 
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org" <kuba@...nel.org>, 
	"pabeni@...hat.com" <pabeni@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH net-next] rswitch: Add PM ops

Hi Shimoda-san,

On Fri, Oct 13, 2023 at 10:55 AM Yoshihiro Shimoda
<yoshihiro.shimoda.uh@...esas.com> wrote:
> > From: Geert Uytterhoeven, Sent: Friday, October 13, 2023 4:29 PM
> > On Fri, Oct 13, 2023 at 4:10 AM Yoshihiro Shimoda
> > <yoshihiro.shimoda.uh@...esas.com> wrote:
> > > > From: Geert Uytterhoeven, Sent: Thursday, October 12, 2023 9:35 PM
> > > > On Thu, Oct 12, 2023 at 2:16 PM Yoshihiro Shimoda
> > > > <yoshihiro.shimoda.uh@...esas.com> wrote:
> > > > > Add PM ops for Suspend to Idle. When the system suspended,
> > > > > the Ethernet Serdes's clock will be stopped. So, this driver needs
> > > > > to re-initialize the Ethernet Serdes by phy_init() in
> > > > > renesas_eth_sw_resume(). Otherwise, timeout happened in phy_power_on().
> > > > >
> > > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>

> > > > > --- a/drivers/net/ethernet/renesas/rswitch.c
> > > > > +++ b/drivers/net/ethernet/renesas/rswitch.c
> > > > > @@ -1991,11 +1993,52 @@ static void renesas_eth_sw_remove(struct platform_device *pdev)
> > > > >         platform_set_drvdata(pdev, NULL);
> > > > >  }
> > > > >
> > > > > +static int __maybe_unused renesas_eth_sw_suspend(struct device *dev)
> > > > > +{
> > > > > +       struct rswitch_private *priv = dev_get_drvdata(dev);
> > > > > +       struct net_device *ndev;
> > > > > +       int i;
> > > >
> > > > unsigned int (also below)
> > >
> > > I don't know why unsigned int is needed. Other functions use
> >
> > There's this old mantra "prefer unsigned over signed in C",
> > and a valid port array index here is always unsigned.
>
> I understood it.
>
> > > rswitch_for_each_enabled_port{_continue_reverse}() with int.
> > > Especially, rswitch_for_each_enabled_port_continue_reverse()
> > > has the following code, unsigned int will not work correctly:
> >
> > Oh, there is also a reverse variant, which indeed needs a signed
> > iterator, currently...
> >
> > > ---
> > > #define rswitch_for_each_enabled_port_continue_reverse(priv, i) \
> > >         for (i--; i >= 0; i--)                                  \
> >
> > I think this can be made to work with an unsigned iterator using
> >
> >     for (; i-- > 0; )
>
> I think that this loop cannot access index 0 :)

rswitch_for_each_enabled_port_continue_reverse() is meant to be
used in the error path, to tear down all ports that were initialized
succesfully? So i is always the index of the first port that failed to
initialize, i.e. i > 0 on entry.

See "git grep -Ww rswitch_for_each_enabled_port_continue_reverse".

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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