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

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Date:   Tue, 14 Jan 2020 09:06:19 +0000
From:   Pawel Laszczak <pawell@...ence.com>
To:     Peter Chen <hzpeterchen@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     "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.

Hi Peter, 

I'm sorry for that.

BTW. I need postpone sending the next version of this patch because there is some issue with synchronization of repositories  regarding the patch "usb: cdns3: Add streams support to cadence USB3 DRD driver"
I don't want generate new conflicts. 

Regards,
Pawell
>
>Peter