netdev - Re: [PATCH v2 1/3] can: c_can_platform: Fix c_can_hw_raminit

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Date:	Tue, 9 Sep 2014 09:51:16 -0500
From:	Nishanth Menon <nm@...com>
To:	Roger Quadros <rogerq@...com>, <wg@...ndegger.com>,
	<mkl@...gutronix.de>
CC:	<tony@...mide.com>, <tglx@...utronix.de>, <mugunthanvnm@...com>,
	<george.cherian@...com>, <balbi@...com>, <nsekhar@...com>,
	<sergei.shtylyov@...entembedded.com>, <linux-omap@...r.kernel.org>,
	<linux-can@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] can: c_can_platform: Fix c_can_hw_raminit_ti()
 and add timeout

On 09/09/2014 09:45 AM, Roger Quadros wrote:
[...]
>>>  	/* We look only at the bits of our instance. */
>>>  	val &= mask;
>>> -	while ((readl(priv->raminit_ctrlreg) & mask) != val)
>>> +	while ((readl(priv->raminit_ctrlreg) & mask) != val) {
>>>  		udelay(1);
>>> +		timeout++;
>>> +
>>> +		if (timeout == 1000) {
>>
>> How did we come up with this number?
> 
> wild guess ;), that it should be set in a few microseconds and the delay is not too
> large.
> 
> Till I don't hear from hardware guys, it will remain a guess.
> 

in cases like these, I suggest using emperical data as point ->
example doing some 10,000 iterations of the operation and picking up
the worse case number and double it.

Either way, you need to document the same, else a few years down the
line, when that number is in question, no one will know what it's
basis was..


-- 
Regards,
Nishanth Menon
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