netdev - Re: [PATCH v3 5/5] r8152: Block future register access if register access fails

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Message-ID: <CAD=FV=U4rGozXHoK8+ejPgRtyoACy1971ftoatQivqzk2tk5ng@mail.gmail.com>
Date: Mon, 16 Oct 2023 09:46:39 -0700
From: Doug Anderson <dianders@...omium.org>
To: Hayes Wang <hayeswang@...ltek.com>
Cc: Jakub Kicinski <kuba@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Alan Stern <stern@...land.harvard.edu>, Simon Horman <horms@...nel.org>, 
	Edward Hill <ecgh@...omium.org>, Laura Nao <laura.nao@...labora.com>, 
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, Grant Grundler <grundler@...omium.org>, 
	Bjørn Mork <bjorn@...k.no>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 5/5] r8152: Block future register access if register
 access fails

Hi,

On Mon, Oct 16, 2023 at 2:16 AM Hayes Wang <hayeswang@...ltek.com> wrote:
>
> Douglas Anderson <dianders@...omium.org>
> > Sent: Friday, October 13, 2023 3:25 AM
> [...]
> >  static int generic_ocp_read(struct r8152 *tp, u16 index, u16 size,
> > @@ -8265,6 +8353,19 @@ static int rtl8152_pre_reset(struct usb_interface
> > *intf)
> >         if (!tp)
> >                 return 0;
> >
> > +       /* We can only use the optimized reset if we made it to the end of
> > +        * probe without any register access fails, which sets
> > +        * `PROBED_WITH_NO_ERRORS` to true. If we didn't have that then return
> > +        * an error here which tells the USB framework to fully unbind/rebind
> > +        * our driver.
>
> Would you stay in a loop of unbind and rebind,
> if the control transfers in the probe() are not always successful?
> I just think about the worst case that at least one control always fails in probe().

We won't! :-) One of the first things that rtl8152_probe() does is to
call rtl8152_get_version(). That goes through to
rtl8152_get_version(). That function _doesn't_ queue up a reset if
there are communication problems, but it does do 3 retries of the
read. So if all 3 reads fail then we will permanently fail probe,
which I think is the correct thing to do.

I can update the comment in __rtl_get_hw_ver() to make it more obvious
that this is by design?

>
> > +        */
> > +       mutex_lock(&tp->control);
>
> I don't think you need the mutex for testing the bit.

Sure, I'll remove it.


> > +       if (!test_bit(PROBED_WITH_NO_ERRORS, &tp->flags)) {
> > +               mutex_unlock(&tp->control);
> > +               return -EIO;
> > +       }
> > +       mutex_unlock(&tp->control);
> > +
> >         netdev = tp->netdev;
> >         if (!netif_running(netdev))
> >                 return 0;
> > @@ -8277,7 +8378,9 @@ static int rtl8152_pre_reset(struct usb_interface
> > *intf)
> >         napi_disable(&tp->napi);
> >         if (netif_carrier_ok(netdev)) {
> >                 mutex_lock(&tp->control);
> > +               set_bit(IN_PRE_RESET, &tp->flags);
> >                 tp->rtl_ops.disable(tp);
> > +               clear_bit(IN_PRE_RESET, &tp->flags);
> >                 mutex_unlock(&tp->control);
> >         }
> >
> > @@ -8293,6 +8396,10 @@ static int rtl8152_post_reset(struct usb_interface
> > *intf)
> >         if (!tp)
> >                 return 0;
> >
> > +       mutex_lock(&tp->control);
>
> I don't think clear_bit() needs the protection of mutex.
> I think you could call rtl_set_accessible() directly.

Agreed, I'll take this out.


Unless something else comes up, I'll send a new version tomorrow with
the above small changes.

-Doug