linux-kernel - Re: [PATCH V2 22/23] pci, acpi: Match PCI config space accessors against platfrom specific quirks.

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Date:	Fri, 08 Jan 2016 09:16:21 -0500
From:	Mark Salter <msalter@...hat.com>
To:	Tomasz Nowicki <tn@...ihalf.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
Subject: Re: [PATCH V2 22/23] pci, acpi: Match PCI config space accessors
 against platfrom specific quirks.

On Wed, 2015-12-16 at 16:16 +0100, Tomasz Nowicki wrote:
> Some platforms may not be fully compliant with generic set of PCI config
> accessors. For these cases we implement the way to overwrite accessors
> set before PCI buses enumeration. Algorithm that overwrite accessors
> matches against platform ID (DMI), domain and bus number, hopefully
> enough for all cases. All quirks can be defined using:
> DECLARE_ACPI_MCFG_FIXUP() and keep self contained.
> 
> example:
> 
> static const struct dmi_system_id yyy[] = {
>         {
>                 .ident = "<Platform ident string>",
>                 .callback = <handler>,
>                 .matches = {
>                         DMI_MATCH(DMI_SYS_VENDOR, "<system vendor>"),
>                         DMI_MATCH(DMI_PRODUCT_NAME, "<product name>"),
>                         DMI_MATCH(DMI_PRODUCT_VERSION, "product version"),
>                 },
>         },
>         { }
> };
> 

This seems awkward to me in the case where the quirk is SoC-based and there
may be multiple platforms affected. Needing a DECLARE_ACPI_MCFG_FIXUP for
each platform using such a SoC (i.e. Mustang and Moonshot) doesn't seem
right. In that case, I think it'd be better to check CPUID and possibly
some SoC register to cover all platforms affected.

Also, there doesn't seem to be a way to connect a given quirk check to the
MCFG/device requesting the ops. So if there is a platform with multiple PCIE
roots and not all of them have quirks, how does one no whether to override the
default ecam ops?