From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nishanth Menon <nm@ti.com>
Subject: Re: [PATCH v2 1/3] can: c_can_platform: Fix c_can_hw_raminit_ti()
 and add timeout
Date: Tue, 9 Sep 2014 09:51:16 -0500
Message-ID: <540F13E4.7020907@ti.com>
References: <1410273070-22485-1-git-send-email-rogerq@ti.com> <1410273070-22485-2-git-send-email-rogerq@ti.com> <540F0FEE.2040202@ti.com> <540F1294.9080107@ti.com>
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To: Roger Quadros <rogerq@ti.com>, wg@grandegger.com, mkl@pengutronix.de
Cc: tony@atomide.com, tglx@linutronix.de, mugunthanvnm@ti.com, george.cherian@ti.com, balbi@ti.com, nsekhar@ti.com, sergei.shtylyov@cogentembedded.com, linux-omap@vger.kernel.org, linux-can@vger.kernel.org, netdev@vger.kernel.org
List-Id: linux-can.vger.kernel.org

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