linux-kernel - Re: [PATCH v9 3/6] pci:host: Add Altera PCIe host controller driver

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Message-ID: <CAFiDJ59ZZ5TBZJ8wauEzP3Je=DeSaGG-PWvm87dkSLfjmyRwjQ@mail.gmail.com>
Date:	Wed, 14 Oct 2015 18:01:46 +0800
From:	Ley Foon Tan <lftan@...era.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Russell King <linux@....linux.org.uk>,
	Marc Zyngier <marc.zyngier@....com>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v9 3/6] pci:host: Add Altera PCIe host controller driver

On Wed, Oct 14, 2015 at 5:36 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 14 October 2015 17:28:45 Ley Foon Tan wrote:
>> On Wed, Oct 14, 2015 at 5:09 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> > On Wednesday 14 October 2015 16:32:25 Ley Foon Tan wrote:
>> >> On Wed, Oct 14, 2015 at 4:20 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> >> > On Wednesday 14 October 2015 10:41:29 Ley Foon Tan wrote:
>> >> >> +static int altera_pcie_remove(struct platform_device *pdev)
>> >> >> +{
>> >> >> +     struct altera_pcie *pcie = platform_get_drvdata(pdev);
>> >> >> +
>> >> >> +     altera_pcie_free_irq_domain(pcie);
>> >> >> +     platform_set_drvdata(pdev, NULL);
>> >> >> +     return 0;
>> >> >> +}
>> >> >
>> >> > I just noticed this. Does it actually work to unload the module
>> >> > and tear down all the pci_dev structures in a safe way?
>> >> Good catch. It only can be compiled as builtin-moduley now, so we can
>> >> remove this _remove callback function.
>> >
>> > I think we should change both: make it possible to load the
>> > driver dynamically, and remove the altera_pcie_remove function.
>> This driver depends on the pci fixups to work correctly. But, fixups
>> callback functions in this driver are not being call if the driver is
>> loadable module.
>
> Ah, I see. We should find a better way to deal with this, as we
> are getting an increasing number of host driver specific fixups.
>
> Bjorn, do you have any idea here?
>
> Could we perhaps have a helper function that lets us register
> fixups dynamically?
>
>> The linker script keeps all pci fixup callbacks in pci fixup regions
>> during kernel compile time. So, it needs to be builtin module. Do you
>> know any way we can update those fixup regions?
>
> The only method I'm aware of at the moment is move the fixups to
> drivers/pci/quirks.c and enclose them in an #ifdef if you want them
> to not appear in kernels that don't support your SoC.
By looking at the drivers/pci/quirks.c, it looks like it is mainly for
the pci endpoint devices.
Fixups for host controller are in the driver itself.

>
>> > You can prevent the module from being unloaded if you also remove
>> > the module_platform_driver() directive and add a module_init()
>> > without a matching module_exit().
>> >
>> > Please also add a '.suppress_bind_attrs = true,' flag in the driver
>> > struct to prevent manual unbinding.
>> I think we don't need these if it only can work as builtin module.
>
> No, this is orthogonal, you need it either way, as built-in drivers
> can still be unbound by writing to sysfs. Try writing the device name
> to /sys/bus/platform/drivers/altera-pcie/unbind and watch it blow up ;-)
Oh I see. Will update with your suggestion.

Thanks.

Regards
Ley Foon
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