Re: [RFC PATCH v1] usb: dwc2: reduce dwc2 driver probe time

[Roy <yunzhi.li@foxmail.com>]

Hi John Youn:

     Could you please give some suggestions from your point of view, 
about this probe time issue ?

     Thanks a lot.

at 2015/2/11 2:23, Julius Werner wrote:
>> @@ -2703,7 +2703,7 @@ int dwc2_get_hwparams(struct dwc2_hsotg *hsotg)
>>          gusbcfg = readl(hsotg->regs + GUSBCFG);
>>          gusbcfg &= ~GUSBCFG_FORCEHOSTMODE;
>>          writel(gusbcfg, hsotg->regs + GUSBCFG);
>> -       usleep_range(100000, 150000);
>> +       usleep_range(25000, 50000);
> The point of usleep_range() is to coalesce multiple timer interrupts
> in idle systems for power efficiency. It's pretty pointless/harmful
> during probe anyway and there's almost never a reason to make the span
> larger than a few milliseconds. You should reduce this to something
> reasonable (e.g. usleep_range(25000, 26000) or even
> usleep_range(25000, 25000)) to save another chunk of time. Same
> applies to other delays above.
>
>> do you know what's the upper boundary for AHB clock ? How fast can it
>> be? It's not wise to change timers because "it works on my RK3288
>> board", you need to guarantee that this won't break anybody else.
> But this code is already a loop that spins on the AHBIdle bit, right?
> It should work correctly regardless of the delay. The only question is
> whether the code could be more efficient with a longer sleep... but
> since the general recommendation is to delay for ranges less than
> 10us, and the AHB clock would need to be lower than 100KHz (the ones I
> see are usually in the range of tens or hundreds of MHz) to take
> longer than that, this seems reasonable to me.
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-- 
--------
Roy Li @ Rockchip