linux-kernel - Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS

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Date:	Mon, 26 Apr 2010 14:07:51 -0700
From:	Yinghai <yinghai.lu@...cle.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Andy Isaacson <adi@...apodia.org>,
	"R. Andrew Bailey" <bailey@...mai.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, guenter.roeck@...csson.com,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Renninger <trenn@...e.de>, yaneti@...lera.com
Subject: Re: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS_END

On 04/26/2010 01:37 PM, Jesse Barnes wrote:
> On Mon, 26 Apr 2010 14:27:56 -0600
>> I think it also leads to at least one problem: Guenter's machine has no
>> VGA but has a PCI device that lives at 0xa0000.  The driver for that
>> device won't be able to request that region if the arch code has marked
>> it busy.
> 
> Ah good point, so we'll want another approach at any rate.  Yinghai?

With current linus's tree, there is some difference between mmio > 1M and MMIO < 1M.

Actually it does not care about E820_RESERVED for > 1M range, because it doesn't have _BUSY.

For < 1M range, 
a. MMIO is not with E820_RESERVED, the device driver will work.
b. MMIO is with E820_RESERVED, the device driver can not reserve it's mmio later. because that MMIO could have parent resource with "reserved" name and _BUSY flag

My patch -v3 will break a.
but my patch -v4 patch will make it work.

but looks -v4 is too tricky.

maybe we just need remove change like following.

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 7bca3c6..9849824 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1094,7 +1094,7 @@ void __init e820_reserve_resources(void)
 		 * pci device BAR resource and insert them later in
 		 * pcibios_resource_survey()
 		 */
-		if (e820.map[i].type != E820_RESERVED || res->start < (1ULL<<20)) {
+		if (e820.map[i].type != E820_RESERVED) {
 			res->flags |= IORESOURCE_BUSY;
 			insert_resource(&iomem_resource, res);
 		}

May need Linus to ack it.

Those strange devices could be some kind of virtual debug devices. and they like to use those low mmio range.

YH
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