linux-kernel - Re: [RFC PATCH] PCI: rockchip: fix system hang up if activate CONFIG_DEBUG

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Date:   Thu, 10 Aug 2017 17:25:17 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Shawn Lin <shawn.lin@...k-chips.com>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Heiko Stuebner <heiko@...ech.de>, linux-pci@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [RFC PATCH] PCI: rockchip: fix system hang up if activate CONFIG_DEBUG_SHIRQ

Hi shawn,

On 08/10/2017 05:14 PM, Shawn Lin wrote:
> Hi Jeffy
>
> On 2017/8/10 16:39, jeffy wrote:
>> Hi shawn,
>>
>> On 08/10/2017 04:21 PM, Shawn Lin wrote:
>>> With CONFIG_DEBUG_SHIRQ enabled, the irq tear down routine
>>> would still access the irq handler registed as a shard irq.
>>> Per the comment within the function of __free_irq, it says
>>> "It's a shared IRQ -- the driver ought to be prepared for
>>> an IRQ event to happen even now it's being freed". However
>>> when failing to probe the driver, it may disable the clock
>>> for accessing the register and the following check for shared
>>> irq state would call the irq handler which accesses the register
>>> w/o the clk enabled. That will hang the system forever.
>>
>> i think this extra irq call is to make sure it's safe to get a shared
>> irq when we are freeing it, and we would not get this irq after freed it.
>>
>> so maybe just call devm_free_irq before disable clks(and other
>> required resources for the irq handler)? and also do it in the
>> rockchip_pcie_remove.
>
> That works since we free it and the following devm_irq_release would
> bail out early. But I know sure if it is the real intention of  the
> devm_  irq stuff,  although devm_free_irq should be called to free the
> IRQ separately if we want. At least that is so explicit that folks will
> know that, as more from the top view, it seems only a little drivers
> there call devm_free_irq for this case by looking into some more
> drivers(Still no any PCIe drivers do that).
>
> Not sure if their systems are robust enough that could access the
> register w/o clk, even without power domain enabled.

maybe we can use request_irq & free_irq directly?