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

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Message-ID: <6adb0f7c-1b1b-4384-b9af-7c3c50e16147@amd.com>
Date: Mon, 15 Jul 2024 13:30:36 -0400
From: Stewart Hildebrand <stewart.hildebrand@....com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
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>, LKML
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] x86: PCI: preserve IORESOURCE_STARTALIGN
 alignment

On 7/10/24 10:05, Ilpo Järvinen wrote:
> On Tue, 9 Jul 2024, Stewart Hildebrand wrote:
> 
>> Currently, it's not possible to use the IORESOURCE_STARTALIGN flag on
>> x86 due to the alignment being overwritten in
>> pcibios_allocate_dev_resources(). Make one small change in arch/x86 to
>> make it work on x86.
>>
>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@....com>
>> ---
>> RFC: We don't have enough info in this function to re-calculate the
>>      alignment value in case of IORESOURCE_STARTALIGN. Luckily our
>>      alignment value seems to be intact, so just don't touch it...
>>      Alternatively, we could call pci_reassigndev_resource_alignment()
>>      after the loop. Would that be preferable?
>> ---
>>  arch/x86/pci/i386.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> 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;
>> +						}
>>  					}
>>  				}
>>  			}
>>
> 
> As a general comment to that loop in pcibios_allocate_dev_resources() 
> function, it would be nice to reverse some of the logic in the if 
> conditions and use continue to limit the runaway indentation level.

The similar function pcibios_allocate_resources() in
arch/powerpc/kernel/pci-common.c has moved some of the logic out into a
separate function. I'll do the same here.