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From:   Felipe Balbi <balbi@kernel.org>
To:     Peter Chen <peter.chen@nxp.com>,
        Peter Chen <hzpeterchen@gmail.com>,
        "pawell\@cadence.com" <pawell@cadence.com>
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        "rogerq\@ti.com" <rogerq@ti.com>,
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        "pjez\@cadence.com" <pjez@cadence.com>,
        "kurahul\@cadence.com" <kurahul@cadence.com>
Subject: RE: [PATCH v1 2/2] usb:cdns3 Add Cadence USB3 DRD Driver
In-Reply-To: <VI1PR04MB5327B1CB6C6BC7D293701F1D8BA70@VI1PR04MB5327.eurprd04.prod.outlook.com>
References: <1544445555-17325-1-git-send-email-pawell@cadence.com> <1544445555-17325-3-git-send-email-pawell@cadence.com> <87h8fkmfar.fsf@linux.intel.com> <BYAPR07MB47095110AF28CC11B4C9E144DDA60@BYAPR07MB4709.namprd07.prod.outlook.com> <CAL411-ryK2LLZVg5_sLkCYOuhwdHLVm5XavSyC9nbEXZah_43w@mail.gmail.com> <877egfmdxk.fsf@linux.intel.com> <VI1PR04MB5327B1CB6C6BC7D293701F1D8BA70@VI1PR04MB5327.eurprd04.prod.outlook.com>
Date:   Wed, 12 Dec 2018 10:34:24 +0200
Message-ID: <871s6nm9db.fsf@linux.intel.com>
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Peter Chen <peter.chen@nxp.com> writes:
>> >> >> +    irqreturn_t ret =3D IRQ_NONE;
>> >> >> +    unsigned long flags;
>> >> >> +    u32 reg;
>> >> >> +
>> >> >> +    priv_dev =3D cdns->gadget_dev;
>> >> >> +    spin_lock_irqsave(&priv_dev->lock, flags);
>> >> >
>> >> >you're already running in hardirq context. Why do you need this lock
>> >> >at all? I would be better to use the hardirq handler to mask your
>> >> >interrupts, so they don't fire again, then used the top-half
>> >> >(softirq) handler to actually handle the interrupts.
>> >>
>> >
>> > This controller may be ran at SMP environment, register and flag
>> > access needs to be protected among CPUs running.
>>=20
>> in hardirq context? When interrupts are already disabled?
>
> Interrupt handler (hardirq context) at CPU0, and process at CPU1, eg
> role switch, unload module, etc.

the process at CPU1 would need to disable interrupts (spin_lock_irq() or
spin_lock_irqsave()), not the hardirq on CPU0 as that already runs with
interrrupts disabled.

https://www.kernel.org/doc/html/latest/kernel-hacking/locking.html#table-of=
-minimum-requirements

=2D-=20
balbi

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