PXA: Handling of UDC with no VBUS pins

[dbaryshkov@gmail.com (Dmitry Eremin-Solenikov)]

On Sun, May 22, 2011 at 12:51 PM, Robert Jarzmik <robert.jarzmik@free.fr> wrote:
> On 05/21/2011 08:35 PM, Dmitry Eremin-Solenikov wrote:
>>
>> My question is what would be better: to extend gpio-vbus to work w/o
>>>>
>>>> VBUS pin or to write new transceiver driver only handling gpio-pullup?
>>>
>>> My personnal feeling is neither, let them be. The generic pullup would
>>> have to ask itself :
>>> ? ?- should the pullup be applied on D+ (on USB 2.0 and 3.0 devices) ?
>>> ? ?- should the pullup be applied on D- (on USB 1.1 devices) ?
>>
>> gpio-vbus driver doesn't do this. It simply handles D+ pullup. I think I'd
>> start with simple D+ pullup driver and the one may add D- functionality
>> if required.
>
> OK, as long as you don't touch the code in pxa27x_udc.c.

Let's do it step by step. My plan would be to drop all non-tranceiver code
for handling pullup and VBUS from both pxa25x_udc and pxa27x_udc.

>>>
>>> The common driver will have to handle the suspend/resume in an
>>> homogenous way.
>>
>> Do pxa25x_udc/pxa27x_udc handle pullup during suspend/resume?
>
> At least pxa27x_udc does, on suspend to RAM (you should look at
> pxa_udc_suspend()).

I see... Thanks for pointing to it.

>>>
>>> If the gadget driver is removed, the pullup should be pulled low.
>>>
>>> All of this work for only 2 drivers looks overkill to me.
>>
>> 3 boards only from PXA. I don't know about other platforms/soc-families.
>
> One other point I've forgotten is that pxa27x_udc in its current state only
> supports gpio pullup/pulldown (ie. an external transciever handles D+
> stimulation). But the PXA sillicon has an internal transciever which can be
> handled directly by pxa27x_udc (register UP2OCR).
>
> Now, nobody uses it. If a board manufacturer is crazy enough to use it, the
> pullup can only be done from inside the pxa27x_udc driver (IO mappings
> driving).

Actually I've thought about this. At least several boards use UP2OCR
handling (balloon3, collibri, cm-x300, em-x270, spitz, stargate, voipac, zeus).

> I still think this driver is a bad idea. But if you wish to do it, go ahead.
> The only thing I'll block is removing the existing pullup code from
> pxa27x_udc.c.

Even if I provide full replacement (from the pulldown-on-suspend POV)?

-- 
With best wishes
Dmitry