linux-kernel - Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability

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Date:   Wed, 25 Jan 2017 15:38:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, tglx@...utronix.de,
        linux-usb@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability

On Wed, Jan 25, 2017 at 08:27:38PM +0800, Lu Baolu wrote:
> In my driver, udelay() is mostly used to handle time out.
> 
> Xdbc hides most USB things in its firmware. Early printk driver only needs
> to setup the registers/data structures and wait until link ready or time out.
> Without udelay(), I have no means to convert the polling times into waiting
> time.

What is timeout and why? If there is an error other than !ready, I would
expect the hardware to inform you of this through another status bit,
no?

So why can't you poll indefinitely for either ready or error?