linux-kernel - Re: [PATCH v2 2/2] phy: intel: Add Keem Bay USB PHY support

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Date:   Wed, 11 Nov 2020 11:49:33 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Wan Mohamad, Wan Ahmad Zainie" 
        <wan.ahmad.zainie.wan.mohamad@...el.com>
Cc:     "kishon@...com" <kishon@...com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "mgross@...ux.intel.com" <mgross@...ux.intel.com>,
        "Raja Subramanian, Lakshmi Bai" 
        <lakshmi.bai.raja.subramanian@...el.com>
Subject: Re: [PATCH v2 2/2] phy: intel: Add Keem Bay USB PHY support

On Wed, Nov 11, 2020 at 09:28:34AM +0000, Wan Mohamad, Wan Ahmad Zainie wrote:
> > From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Sent: Monday, November 9, 2020 7:41 PM
> > To: Wan Mohamad, Wan Ahmad Zainie
> > On Mon, Nov 09, 2020 at 11:16:54AM +0800, Wan Ahmad Zainie wrote:

...

> > > +	usleep_range(30, 50);
> > 
> > Why 30-50?
> 
> I take this value from boot firmware.
> There is a delay of 30us after clearing IDDQ_enable bit.
> I believe the purpose is to ensure all analog blocks are powered up.

Then put it into comment.

...

> > > +	usleep_range(20, 50);
> > 
> > Why these numbers?
> 
> In Keem Bay data book, under USB initialization section,
> there is step that there must be a minimum 20us wait
> after clock enable, before bringing PHYs out of reset.
> 
> 50 is the value that I picked randomly. Is usleep_range(20, 20)
> Better?

No, the better as I told you already few times is to comment "why?" these
numbers. Above can be like:
"According to datasheet this step requires 20us wait..."

...

> > > +	usleep_range(2, 10);
> > 
> > Ditto.
> 
> Under the same section above, there is a step for 2us wait.
> I believe it is for register write to go through.

Ditto.

> > 
> > ...
> > 
> > > +	usleep_range(20, 50);
> > 
> > Ditto.
> 
> Under the same section above, there is a step to wait 20us
> after setting SRAM load bit, before release the controller
> reset.
> 
> I will add comment for those 4 delay above.

Yes, please.

...

> Before I proceed with v3, I would like to know if I should
> use udelay(), instead of usleep_range()?
> I refer to https://www.kernel.org/doc/Documentation/timers/timers-howto.txt.

You should know your code better than me. That howto is clear about when of
which API calls can be used.

-- 
With Best Regards,
Andy Shevchenko