linux-kernel - Re: [PATCH 6/10] watchdog: bcm63xx_wdt: Obtain watchdog clock HZ from "periph" clk

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Date:	Mon, 23 Nov 2015 19:00:28 +0000
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Florian Fainelli <f.fainelli@...il.com>,
	Jonas Gorski <jogo@...nwrt.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Kevin Cernekee <cernekee@...il.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	MIPS Mailing List <linux-mips@...ux-mips.org>,
	linux-watchdog@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH 6/10] watchdog: bcm63xx_wdt: Obtain watchdog clock HZ from
 "periph" clk

On 23/11/15 18:19, Florian Fainelli wrote:
> On 23/11/15 07:02, Jonas Gorski wrote:
>> On Sun, Nov 22, 2015 at 3:07 PM, Simon Arlott <simon@...e.lp0.eu> wrote:
>>> -#define WDT_HZ                 50000000                /* Fclk */
>>> +#define WDT_CLK_NAME           "periph"
>> 
>> @Florian:
>> Is this correct? The comment for the watchdog in 6358_map_part.h and
>> earlier claims that the clock is 40 MHz there, but the code uses 50MHz
>> - is this a bug in the comments or is it a bug taken over from the
>> original broadcom code? I'm sure that the periph clock being 50 MHz
>> even on the older chips is correct, else we'd have noticed that in
>> serial output (where it's also used).
> 
> There are references to a Fbus2 clock in documentation, but I could not
> find any actual documentation for its actual clock frequency, I would be
> surprised if this chip would have diverged from the previous and future
> ones and used a 40Mhz clock. 6345 started with a peripheral clock
> running at 50Mhz, and that is true for all chips since then AFAICT.
> 
> I agree we would have noticed this with the UART or SPI controllers if
> that was not true, so probably a code glitch here...

I've tested both the timer and the watchdog and they give near perfect
time intervals (within 1-2ms based on printk times over serial) so it'd
be obvious if they were out by 25%.

-- 
Simon Arlott
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