linux-kernel - Re: [PATCH] x86/pci: do assign root bus res if

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Message-ID: <49F61265.10201@kernel.org>
Date:	Mon, 27 Apr 2009 13:15:33 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, Gary Hade <garyhade@...ibm.com>,
	Alex Chiang <achiang@...com>, linux-acpi@...r.kernel.org,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH] x86/pci: do assign root bus res if _CRS is used

Bjorn Helgaas wrote:
> On Monday 20 April 2009 07:35:40 pm Yinghai Lu wrote:
>> it wil be overwriten later if _CRS is used, so don't bother to set it.
>>
>> [ Impact: cleanup ]
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>>
>> ---
>>  arch/x86/pci/amd_bus.c |    4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> Index: linux-2.6/arch/x86/pci/amd_bus.c
>> ===================================================================
>> --- linux-2.6.orig/arch/x86/pci/amd_bus.c
>> +++ linux-2.6/arch/x86/pci/amd_bus.c
>> @@ -100,6 +100,10 @@ void x86_pci_root_bus_res_quirks(struct
>>  	int j;
>>  	struct pci_root_info *info;
>>  
>> +	/* don't go for it if _CRS is used */
>> +	if (pci_probe & PCI_USE__CRS)
>> +		return;
>> +
>>  	/* if only one root bus, don't need to anything */
>>  	if (pci_root_num < 2)
>>  		return;
> 
> This isn't a comment on this patch per se.
> 
> I am concerned about the fact that "pci=use_crs" is not the default.
> From the changelog of 62f420f8282, it sounds like you have to boot an
> IBM x3850 with "pci=use_crs" to make hot-plug work, even though ACPI
> tells us everything we need to know.  That's backwards.
> 
> We shouldn't need an option to tell Linux that the firmware is
> trustworthy.  We should have an option to *ignore* it for the times
> when we trip over something broken and haven't figured out a way to
> work around it yet.

other system may have broken _CRS.

maybe we could try to use DMI whitelist them?

YH
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