Re: [RFC 5/5] USB: Eliminate delays involved in root hub initialization during HNP

[Felipe Balbi <balbi@ti.com>]

On Thu, Dec 16, 2010 at 04:56:15PM +0530, Pavan Kondeti wrote:
>On 12/15/2010 5:51 PM, Felipe Balbi wrote:
>> On Wed, Dec 15, 2010 at 04:44:14PM +0530, Pavankumar Kondeti wrote:
>>> Some USB controllers have common resources (IRQ, register address
>>> space) for Host, Peripheral and OTG.  So HCD is added only before
>>> entering into Host mode.  Root hub initialization is done in
>>> different steps to decrease boot up time.  But this makes B-device
>>> difficult to meet HNP timings.  Hence eliminate delays involved in
>>> root hub initialization for B-host.
>>
>> I wonder if this is the best approach. Would it be easier to not touch
>> usbcore, probe the entire stack during boot but have a "core" layer
>> handling synchronization to shared resources ?
>>
>The implementation is like this:
>
>Actually OTG synchronizes UDC and HCD. OTG driver probe will be called
>first and it takes care of turning on clocks, resetting controller and
>PHY and enabling interrupts (VBUS and Id). UDC and HCD will not modify
>hardware registers in their probe functions. So HCD will not call
>usb_add_hcd() function in it's probe(). After HCD and UDC registers with
>OTG via otg_set_xxx(), OTG activates HCD (by calling usb_add_hcd()) or
>UDC (usb_gadget_connect()) based on Id/VBUS status. When gadget is
>active, HCD is detached from USB core (usb_remove_hcd()). So user space
>can not poke into sysfs/debugfs nodes provided in the usb core.
>
>> Maybe you could make your device an MFD device that allocates
>> platform_devices for its children (HCI, UDC, OTG, etc) and pass in a
>> bunch of read/write functions as platform_data for them to use as
>> accessors to shared register space ?!? Would that work ?
>>
>The easy way to deal this problem is removing HCD when Mini/Micro -A
>cable is detached.

But why do you need to do that isn't clear. What's the problem in
keeping HCD always available ? If it's a mini/micro-B cable you will
enter peripheral role anyway.

-- 
balbi