linux-kernel - Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated

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Message-ID: <2317a4bc-bd4d-53a7-7fa6-87728d5393cd@redhat.com>
Date:   Tue, 29 Jun 2021 08:17:03 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Robinson <pbrobinson@...il.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Michal Simek <michal.simek@...inx.com>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        rfi@...ts.rocketboards.org, Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with
 clocks gated

On 6/29/21 2:38 AM, Bjorn Helgaas wrote:
> On Thu, Jun 24, 2021 at 05:40:40PM -0500, Bjorn Helgaas wrote:

[snip]

>>>
>>> So let's just move all the IRQ init before the pci_host_probe() call, that
>>> will prevent issues like this and seems to be the correct thing to do too.
>>
>> Previously we registered rockchip_pcie_subsys_irq_handler() and
>> rockchip_pcie_client_irq_handler() before the PCIe clocks were
>> enabled.  That's a problem because they depend on those clocks being
>> enabled, and your patch fixes that.
>>
>> rockchip_pcie_legacy_int_handler() depends on rockchip->irq_domain,
>> which isn't initialized until rockchip_pcie_init_irq_domain().
>> Previously we registered rockchip_pcie_legacy_int_handler() as the
>> handler for the "legacy" IRQ before rockchip_pcie_init_irq_domain().
>>
>> I think your patch *also* fixes that problem, right?
> 
> The lack of consistency in how we use
> irq_set_chained_handler_and_data() really bugs me.
> 
> Your patch fixes the ordering issue where we installed
> rockchip_pcie_legacy_int_handler() before initializing data
> (rockchip->irq_domain) that it depends on.
> 
> But AFAICT, rockchip still has the problem that we don't *unregister*
> rockchip_pcie_legacy_int_handler() when the rockchip-pcie module is
> removed.  Doesn't this mean that if we unload the module, then receive 
> an interrupt from the device, we'll try to call a function that is no
> longer present?
> 

Good question, I don't to be honest. I'll have to dig deeper on this but
my experience is that the module removal (and device unbind) is not that
well tested on ARM device drivers in general.

Best regards,
-- 
Javier Martinez Canillas
Software Engineer
New Platform Technologies Enablement team
RHEL Engineering