linux-kernel - Re: [RFC PATCH] x86: Add safe_udelay() and safe

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Date:	Thu, 13 Jan 2011 17:00:56 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg KH <greg@...ah.com>
CC:	Jason Wessel <jason.wessel@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()

On 01/13/2011 04:40 PM, Benjamin Herrenschmidt wrote:
> On Thu, 2011-01-13 at 16:31 -0800, Yinghai Lu wrote:
>> there are some udelay() in drivers/usb/early/ehci-dbgp.c
>>
>> that is for early USB debug port console support.
>>
>> We should replace them with early version udelay()
> 
> Or have a reasonable default for lpj ...

x86 udelay is using percpu cpu_data.loops_per_jiffy, and it is not set yet.

when x86 boot with earlyprintk=dbgp, that early console is loaded quite before setup_percpu_areas()

maybe something like this could workaround it, if cpu_data(0) can be used before setup_percpu_areas().

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d3cfe26..333694a 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -734,6 +734,7 @@ void __init setup_arch(char **cmdline_p)
 
        early_trap_init();
        early_cpu_init();
+       cpu_data(0).loops_per_jiffy = loops_per_jiffy;
        early_ioremap_init();
 
        setup_olpc_ofw_pgd();
--
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