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

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Message-ID: <22e339c1-0ada-0824-cd34-d5779328b522@linux.intel.com>
Date: Wed, 10 Jul 2024 17:05:43 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Stewart Hildebrand <stewart.hildebrand@....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 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.

-- 
 i.