linux-kernel - Re: [PATCH] usb: cdns3: Fix: ARM core hang after connect/disconnect operation.

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Date:   Tue, 14 Jan 2020 16:57:15 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Pawel Laszczak <pawell@...ence.com>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "rogerq@...com" <rogerq@...com>,
        "jbergsagel@...com" <jbergsagel@...com>,
        "nsekhar@...com" <nsekhar@...com>, "nm@...com" <nm@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>,
        Sanket Parmar <sparmar@...ence.com>,
        Peter Chan <peter.chan@....com>
Subject: Re: [PATCH] usb: cdns3: Fix: ARM core hang after connect/disconnect operation.

On Thu, Jan 9, 2020 at 5:39 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Thu, Jan 09, 2020 at 08:34:12AM +0000, Pawel Laszczak wrote:
> > >
> > >On Thu, Jan 09, 2020 at 06:27:02AM +0000, Pawel Laszczak wrote:
> > >> >> +       writel(EP_CMD_EPRST, &priv_dev->regs->ep_cmd);
> > >> >> +
> > >> >> +       ret = readl_poll_timeout_atomic(&priv_dev->regs->ep_cmd, val,
> > >> >> +                                       !(val & (EP_CMD_CSTALL | EP_CMD_EPRST)),
> > >> >> +                                       1, 1000);
> > >> >> +
> > >> >> +       if (unlikely(ret))
> > >> >
> > >> >Unless you can measure the difference of using/not using a
> > >> >unlikely/likely mark, NEVER use it.  The compiler and cpu can almost
> > >> >always do better than you can, we have the tests to prove it.
> > >> >
> > >>
> > >> The both of the above timeout should never occur. If they occurred it would be a
> > >> critical controller bug. In this case driver can only inform  about this event.
> > >
> > >"Should never occur" is a fun thing to say :)
> > >
> > >If it can never occur, then don't even check for it.
> >
> > Yes, on existing platforms it can never occur.
> >
> > >
> > >If it can, then check for it and handle it properly.
> > >
> > >What about this controller in systems with removable busses (like PCI?)
> > >What happens then (hint, I bet this could occur...)
> >
> > It's good question.  Nobody from our customer currently use such system.
> > The only platform with PCI is used by me for testing purpose.
>
> So if you do have a PCI device, then you need to handle PCI reads
> failing and returning all 1s.  Hopefully you can gracefully handle this :)
>
> Adding timeout handling here, where it is totally obvious to do so,
> would be a good thing.
>
> thanks,
>
> greg k-h

Hi Pawel,

My email is: peter.chen@....com, please change it when your send next version.

Peter