linux-kernel - Re: [PATCH 2/3] clocksource: add DB8500 PRCMU Timer support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 31 May 2011 19:00:39 +0200
From:	Mattias Wallin <mattias.wallin@...ricsson.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 2/3] clocksource: add DB8500 PRCMU Timer support

On 05/31/2011 12:38 PM, Thomas Gleixner wrote:
> On Tue, 31 May 2011, Mattias Wallin wrote:
>> +static cycle_t clksrc_db8500_prcmu_read(struct clocksource *cs)
>> +{
>> +	u32 count, count2;
>> +
>> +	do {
>> +		count = readl(PRCMU_TIMER_4_DOWNCOUNT);
>> +		count2 = readl(PRCMU_TIMER_4_DOWNCOUNT);
>> +	} while (count2 != count);
>
> What's the point of this exercise ?
It is a software workaround for a HW bug. If the timer is read exactly 
when the logic is in the process of flipping over to a new value you 
will get wrong value (large deviations). The problem was found running 
LTP tests reporting "Timer going backwards". Reading it two times will 
take long enough for the timer to stabilise according to our HW guys 
measurements.
I agree with you that it is odd enough to deserve a comment in the code. 
I will comment it in next version.
>
>> +	clocksource_calc_mult_shift(&clocksource_db8500_prcmu,
>> +		RATE_32K, SCHED_CLOCK_MIN_WRAP);
>> +	clocksource_register(&clocksource_db8500_prcmu);
>
> Please use clocksource_register_hz()
Ok.
>
>> diff --git a/include/linux/clksrc-db8500-prcmu.h b/include/linux/clksrc-db8500-prcmu.h
>> new file mode 100644
>> index 0000000..42b8587
>> --- /dev/null
>> +++ b/include/linux/clksrc-db8500-prcmu.h
>
> Huch, why needs this to be a separate head in include/linux ?
I will move the header file to mach-ux500/include/mach/. Ok?

(I have long time ago been thought to avoid include mach headers from 
the drivers. But if I understand it correct it is not true any more and 
in this case it certainly makes no sense since I break that rule myself.)
>
>> @@ -0,0 +1,17 @@
>> +/*
>> + * Copyright (C) ST-Ericsson SA 2011
>> + *
>> + * License Terms: GNU General Public License v2
>> + * Author: Mattias Wallin<mattias.wallin@...ricsson.com>
>> + *
>> + */
>> +#ifndef __CLKSRC_DB8500_PRCMU_H
>> +#define __CLKSRC_DB8500_PRCMU_H
>> +
>> +#ifdef CONFIG_CLKSRC_DB8500_PRCMU
>> +void __init clksrc_db8500_prcmu_init(void);
>> +#else
>> +void __init clksrc_db8500_prcmu_init(void) {}
>> +#endif
>> +
>> +#endif
>> --
>> 1.7.4.3
>>
>>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/