linux-kernel - Re: [RFC PATCH 4/6] x86: PCI: preserve IORESOURCE

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Message-ID: <534ef932-a9f7-4d90-88b9-8d9a751cb2f2@amd.com>
Date: Mon, 15 Jul 2024 13:26:14 -0400
From: Stewart Hildebrand <stewart.hildebrand@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Bjorn Helgaas <bhelgaas@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
	<x86@...nel.org>, <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] x86: PCI: preserve IORESOURCE_STARTALIGN
 alignment

On 7/10/24 17:24, Bjorn Helgaas wrote:
> On Wed, Jul 10, 2024 at 12:16:24PM -0400, Stewart Hildebrand wrote:
>> On 7/9/24 12:19, Bjorn Helgaas wrote:
>>> On Tue, Jul 09, 2024 at 09:36:01AM -0400, Stewart Hildebrand wrote:
>>>> diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
>>>> index f2f4a5d50b27..ff6e61389ec7 100644
>>>> --- a/arch/x86/pci/i386.c
>>>> +++ b/arch/x86/pci/i386.c
>>>> @@ -283,8 +283,11 @@ static void pcibios_allocate_dev_resources(struct pci_dev *dev, int pass)
>>>>  						/* We'll assign a new address later */
>>>>  						pcibios_save_fw_addr(dev,
>>>>  								idx, r->start);
>>>> -						r->end -= r->start;
>>>> -						r->start = 0;
>>>> +						if (!(r->flags &
>>>> +						      IORESOURCE_STARTALIGN)) {
>>>> +							r->end -= r->start;
>>>> +							r->start = 0;
>>>> +						}
> 
> I wondered why this only touched x86 and whether other arches need a
> similar change.  This is used in two paths:
> 
>   1) pcibios_resource_survey_bus(), which is only implemented by x86
> 
>   2) pcibios_resource_survey(), which is implemented by x86 and
>   powerpc.  The powerpc pcibios_allocate_resources() is similar to the
>   x86 pcibios_allocate_dev_resources(), but powerpc doesn't have the
>   r->end and r->start updates you're making conditional.

Actually it does. It's in a separate function, alloc_resource(). I'll
make the change over there too.

> So it looks like x86 is indeed the only place that needs this change.
> None of this stuff is arch-specific, so it's a shame that we don't
> have generic code for it all.  Sigh, oh well.
> 
>>>>  					}
>>>>  				}
>>>>  			}
>>>> -- 
>>>> 2.45.2
>>>>
>>