linux-kernel - Re: [PATCH 1/3] pci: determine CLS more intelligently

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Message-ID: <20090704092956.GA26456@elte.hu>
Date:	Sat, 4 Jul 2009 11:29:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	Greg KH <greg@...ah.com>, Robert Hancock <hancockr@...w.ca>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-pci@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Daniel Ritz <daniel.ritz@....ch>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Axel Birndt <towerlexa@....de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 1/3] pci: determine CLS more intelligently


* Tejun Heo <tj@...nel.org> wrote:

> Till now, CLS has been determined either by arch code or as 
> L1_CACHE_BYTES.  Only x86 and ia64 set CLS explicitly and x86 
> doesn't always get it right.  On most configurations, the chance 
> is that firmware configures the correct value during boot.
> 
> This patch makes pci_init() determine CLS by looking at what 
> firmware has configured.  It scans all devices and if all non-zero 
> values agree, the value is used.  If none is configured or there 
> is a disagreement, pci_dfl_cache_line_size is used.  arch can set 
> the dfl value (via PCI_CACHE_LINE_BYTES or 
> pci_dfl_cache_line_size) or override the actual one.
> 
> ia64, x86 and sparc64 updated to set the default cls instead of 
> the actual one.
> 
> While at it, declare pci_cache_line_size and 
> pci_dfl_cache_line_size in pci.h and drop private declarations 
> from arch code.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Acked-by: David Miller <davem@...emloft.net>
> Acked-by: Greg KH <gregkh@...e.de>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tony Luck <tony.luck@...el.com>

The principle looks good to me. Regressions could be expected though 
- these details are fragile and affect the way how we talk to 
hardware.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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