linux-kernel - Re: raw_pci_read in quirk_intel

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Message-ID: <20080211074954.GA11388@colo.lackof.org>
Date:	Mon, 11 Feb 2008 00:49:54 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yinghai Lu <yhlu.kernel@...il.com>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Tony Camuso <tcamuso@...hat.com>,
	Grant Grundler <grundler@...isc-linux.org>,
	Loic Prylli <loic@...i.com>, Adrian Bunk <bunk@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>,
	linux-pci@...ey.karlin.mff.cuni.cz, Martin Mares <mj@....cz>
Subject: Re: raw_pci_read in quirk_intel_irqbalance

On Sun, Feb 10, 2008 at 10:04:16PM -0700, Matthew Wilcox wrote:
> > "A disabled or non-existent device's configuration register space is
> > hidden. A disabled or non-existent device will return all ones for reads
> > and will drop writes just as if the cycle terminated with a Master Abort
> > on PCI."
> 
> I'd like to thank Grant for pointing out to me that this is exactly what
> the write immediately above this is doing -- enabling device 8 to
> respond to config space cycles.

welcome.

...
> >From f565b65591a3f90a272b1d511e4ab1728861fe77 Mon Sep 17 00:00:00 2001
> From: Matthew Wilcox <matthew@....cx>
> Date: Sun, 10 Feb 2008 23:18:15 -0500
> Subject: [PATCH] Use proper abstractions in quirk_intel_irqbalance
> 
> Since we may not have a pci_dev for the device we need to access, we can't
> use pci_read_config_word.  But raw_pci_read is an internal implementation
> detail; it's better to use the architected pci_bus_read_config_word
> interface.  Using PCI_DEVFN instead of a mysterious constant helps
> reassure everyone that we really do intend to access device 8.
> 
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> ---
>  arch/x86/kernel/quirks.c |    9 ++++++---
>  1 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/quirks.c b/arch/x86/kernel/quirks.c
> index 1941482..c47208f 100644
> --- a/arch/x86/kernel/quirks.c
> +++ b/arch/x86/kernel/quirks.c
> @@ -11,7 +11,7 @@
>  static void __devinit quirk_intel_irqbalance(struct pci_dev *dev)
>  {
>  	u8 config, rev;
> -	u32 word;
> +	u16 word;
>  
>  	/* BIOS may enable hardware IRQ balancing for
>  	 * E7520/E7320/E7525(revision ID 0x9 and below)
> @@ -26,8 +26,11 @@ static void __devinit quirk_intel_irqbalance(struct pci_dev *dev)
>  	pci_read_config_byte(dev, 0xf4, &config);
>  	pci_write_config_byte(dev, 0xf4, config|0x2);

Can you also add a comment which points at the Intel documentation?

http://download.intel.com/design/chipsets/datashts/30300702.pdf
Page 34 documents 0xf4 register.

And I just doubled checked that the 0xf4 register value is restored later
in the quirk (obvious when you look at the code but not from the patch).

> -	/* read xTPR register */
> -	raw_pci_read(0, 0, 0x40, 0x4c, 2, &word);
> +	/*
> +	 * read xTPR register.  We may not have a pci_dev for device 8
> +	 * because it might be hidden until the above write.
> +	 */
> +	pci_bus_read_config_word(dev->bus, PCI_DEVFN(8, 0), 0x4c, &word);

Yeah, this should work even though we don't have a dev for it.

Acked-by: Grant Grundler <grundler@...isc-linux.org>

thanks,
grant
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