linux-kernel - RE: [PATCH v1 2/2] usb:cdns3 Add Cadence USB3 DRD Driver

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Date:   Wed, 12 Dec 2018 10:34:24 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Peter Chen <peter.chen@....com>,
        Peter Chen <hzpeterchen@...il.com>,
        "pawell\@cadence.com" <pawell@...ence.com>
Cc:     "devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
        "rogerq\@ti.com" <rogerq@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        "adouglas\@cadence.com" <adouglas@...ence.com>,
        "jbergsagel\@ti.com" <jbergsagel@...com>,
        "nsekhar\@ti.com" <nsekhar@...com>, "nm\@ti.com" <nm@...com>,
        "sureshp\@cadence.com" <sureshp@...ence.com>,
        "pjez\@cadence.com" <pjez@...ence.com>,
        "kurahul\@cadence.com" <kurahul@...ence.com>
Subject: RE: [PATCH v1 2/2] usb:cdns3 Add Cadence USB3 DRD Driver

Peter Chen <peter.chen@....com> writes:
>> >> >> +    irqreturn_t ret = IRQ_NONE;
>> >> >> +    unsigned long flags;
>> >> >> +    u32 reg;
>> >> >> +
>> >> >> +    priv_dev = 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.
>> 
>> 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

-- 
balbi

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