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

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Message-ID: <568FCAD7.70700@arm.com>
Date:	Fri, 8 Jan 2016 08:42:31 -0600
From:	Jeremy Linton <jeremy.linton@....com>
To:	Mark Salter <msalter@...hat.com>, 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:	<jchandra@...adcom.com>, <linaro-acpi@...ts.linaro.org>,
	<linux-pci@...r.kernel.org>, <Liviu.Dudau@....com>,
	<ddaney@...iumnetworks.com>, <linux-kernel@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <robert.richter@...iumnetworks.com>,
	<Suravee.Suthikulpanit@....com>, <jcm@...hat.com>,
	<wangyijing@...wei.com>, <tglx@...utronix.de>, <mw@...ihalf.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2 22/23] pci, acpi: Match PCI config space accessors
 against platfrom specific quirks.

On 01/08/2016 08:16 AM, Mark Salter wrote:
> 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.

...

> 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?

That was the thinking that lead me to quirk the xgene based m400 using
the root bridge VID/DID and DECLARE_PCI_FIXUP_EARLY(). A solution which
works because the default config space accessors work sufficiently to
read the VID/DID.

I think that solution might work for at least one other vendor as well,
and IMHO is better than using DMI for the reasons you list.

I will rebase/post those patches RSN...
















(please ignore the message below, i'm working getting that taken care of
as well)



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