linux-kernel - Re: [PATCH V3 20/21] pci, acpi: Match PCI config space accessors against platfrom specific quirks.

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Message-ID: <569DEBE9.5090909@semihalf.com>
Date:	Tue, 19 Jan 2016 08:55:21 +0100
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	"liudongdong (C)" <liudongdong3@...wei.com>,
	Mark Salter <msalter@...hat.com>, bhelgaas@...gle.com,
	arnd@...db.de, will.deacon@....com, catalin.marinas@....com,
	rjw@...ysocki.net, hanjun.guo@...aro.org,
	Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
	jiang.liu@...ux.intel.com, Stefano.Stabellini@...citrix.com
Cc:	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....com, ddaney@...iumnetworks.com, tglx@...utronix.de,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linaro-acpi@...ts.linaro.org, jchandra@...adcom.com,
	jcm@...hat.com, Zhou Wang <wangzhou1@...ilicon.com>,
	Gabriele Paoloni <gabriele.paoloni@...wei.com>
Subject: Re: [PATCH V3 20/21] pci, acpi: Match PCI config space accessors
 against platfrom specific quirks.

On 19.01.2016 02:49, liudongdong (C) wrote:
> Hi Tomasz, Mark
>
> 在 2016/1/18 20:41, Tomasz Nowicki 写道:
>> On 14.01.2016 16:36, Mark Salter wrote:
>>>> +extern struct pci_mcfg_fixup __start_acpi_mcfg_fixups[];
>>>> >+extern struct pci_mcfg_fixup __end_acpi_mcfg_fixups[];
>>>> >+
>>>> >+static struct pci_ops *pci_mcfg_check_quirks(struct acpi_pci_root
>>>> *root)
>>>> >+{
>>>> >+    struct pci_mcfg_fixup *f;
>>>> >+    int bus_num = root->secondary.start;
>>>> >+    int domain = root->segment;
>>>> >+
>>>> >+    /*
>>>> >+     * First match against PCI topology <domain:bus> then use DMI or
>>>> >+     * custom match handler.
>>>> >+     */
>>>> >+    for (f = __start_acpi_mcfg_fixups; f < __end_acpi_mcfg_fixups;
>>>> f++) {
>>>> >+        if ((f->domain == domain || f->domain ==
>>>> PCI_MCFG_DOMAIN_ANY) &&
>>>> >+            (f->bus_num == bus_num || f->bus_num ==
>>>> PCI_MCFG_BUS_ANY) &&
>>>> >+            (f->system ? dmi_check_system(f->system) : 0 ||
>>>> >+             f->match ? f->match(f, root) : 0))
>>>> >+            return f->ops;
>>> I think this would be better as:
>>>
>>>             (f->system ? dmi_check_system(f->system) : 1 &&
>>>              f->match ? f->match(f, root) : 1))
>>>             return f->ops;
>>>
>>> Otherwise, one has to call dmi_check_system() from f->match() if
>>> access to root is needed.
>>
>
> Non-DMI, we need not to call dmi_check_system() from f->match(),
> we can use _HID to decide to hook the pci_ops or not.

Sorry, but I dont understand your point. Can you elaborate?

With Mark modification, you can use the following cases to identify 
platform:
1. DMI only
2. f->match() only (_HID can be used there)
3. DMI and f->match()

DMI used to be very convenient way to recognise platform, sometimes it 
is not enough, hence f->match() alternative.

Tomasz