linux-kernel - Re: [PATCH 2/2] acpi based pci gap caluculation v2

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Date:	Tue, 24 Jun 2008 21:17:45 -0700
From:	"Alok kataria" <alokkataria1@...il.com>
To:	"Zhao Yakui" <yakui.zhao@...el.com>
Cc:	akataria@...are.com, lenb@...nel.org,
	"Ingo Molnar" <mingo@...e.hu>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] acpi based pci gap caluculation v2

On Tue, Jun 24, 2008 at 7:49 PM, Zhao Yakui <yakui.zhao@...el.com> wrote:
> On Tue, 2008-06-24 at 11:48 -0700, Alok Kataria wrote:
>> Evaluates the _CRS object under PCI0 looking for producer resources.
>> Then searches the e820 memory space for a gap within these producer resources.
>>
>> Allows us to find a gap for the unclaimed pci resources or MMIO resources
>> for hotplug devices within the BIOS allowed pci regions.
>>
> It seems reasonable.
> But if the resource obtained from the PCI0 _CRS method is incorrect, we
> will get the incorrect pci_mem_start.

Hi Yakui,

What do you mean by the PCI0 _CRS being incorrect ? Why would the BIOS
give a incorrect _CRS object ?
Also we don't just take the value given from the _CRS method, we still
read the e820_map to search for an unallocated resource. So even if
(by chance) the _CRS method returns incorrect value we would still
figure out if there is a collision with an already allocated resource.

>
> At the same time after the patch is applied, pci_mem_start will be
> parsed in two different ways.

Yes pci_mem_start would be initialized in 2 different ways but we
still have to parse the e820_map the old way because there could be
systems without ACPI.

> If the result is different, maybe the
> incorrect pci_mem_start will be used.

Yeah, The result is different in my case. Though my BIOS reserves
hotpluggable memory region, kernel doesn't respect that right now and
just parses the e820_map to calculate the gap and pci_mem_start value.
I have explained the problem in this mail.

http://marc.info/?l=linux-acpi&m=121391675711763&w=2

Maybe nobody has seen this problem yet, because there are no systems
out there with less than 4GB memory to start with and which allow
memory hotplug.

But still i don't understand what do you mean by, we can get incorrect
pci_mem_start, in which case ?

Thanks,
Alok
>
> Best regards.
>  Yakui
>>
>>
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