linux-kernel - Re: [PATCH 04/36] x86/pci: add cap

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Date:	Thu, 21 Jan 2010 07:49:17 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 04/36] x86/pci: add cap_resource



On Wed, 20 Jan 2010, Yinghai Lu wrote:
> 
> -v2: hpa said we should compare with (resource_size_t)~0

Hmm. Some of these look dubious.

> diff --git a/arch/x86/pci/bus_numa.c b/arch/x86/pci/bus_numa.c
> index f939d60..b267919 100644
> --- a/arch/x86/pci/bus_numa.c
> +++ b/arch/x86/pci/bus_numa.c
> @@ -60,6 +60,9 @@ void __devinit update_res(struct pci_root_info *info, size_t start,
>  	if (start > end)
>  		return;
>  
> +	if (start == (resource_size_t)~0)
> +		return;

Here, 'start' isn't a resource_size_t. It's a regular size_t. And if 
resource_size_t is u64, and size_t is u32, this test can never be true.

Maybe that is intentional, but if looks odd/wrong. Needs a comment if 
right, needs fixing if wrong.

> +static inline resource_size_t cap_resource(u64 val)
> +{
> +	if (val > (resource_size_t)~0)
> +		return (resource_size_t)~0;
> +	else
> +		return val;
> +}
>  #endif

And this just looks odd. I'd suggest just doing

	#define MAX_RESOURCE ((resource_size_t)~0)

	static inline resource_size_t cap_resource(u64 val)
	{
		if (val > MAX_RESOURCE)
			val = MAX_RESOURCE;
		return val;
	}

instead, which looks a whole lot more natural. No?

			Linus
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