[U-Boot] [UBOOT RFC PATCH 07/13] usb: gadget: g_dnl: Explicitly set the max packet size in descriptor

[Lukasz Majewski <l.majewski@samsung.com>]

Hi Felipe,

> On Tue, Aug 19, 2014 at 09:08:00PM +0530, Kishon Vijay Abraham I
> wrote:
> > 
> > 
> > On Monday 18 August 2014 08:26 PM, Lukasz Majewski wrote:
> > > Hi Kishon,
> > > 
> > >>> Explicity set the max packet size in the device descriptor to
> > >>> 0x40 as specified in the device class specification for device
> > >>> firmware upgrade. Also changed debug to printf to explicitly
> > >>> notify the user if the device has been enumerated.
> > > 
> > > It seems like this patch slipped without my attention ...
> > > 
> > > Hence, I'd like to ask why you must hardcode the packet size here?
> > 
> > http://www.usb.org/developers/devclass_docs/usbdfu10.pdf (in
> > section 4.2.1 DFU Mode Device Descriptor), specifies the
> > bMaxPacketSize0 can be  8,16,32,64. And the value we get from
> > gadget is 512. So hard coded it.
> 
> as I mentioned, this should be changed on connection done interrupt.

In the u-boot it is set up during binding the composite.

> DFU has one of the poorest documentations for a USB Class and has some
> moronic definitions.

Frankly speaking I prefer to have the worst standard than some
"brilliant" in house developed protocols.

> What happens if you want ot run DFU with a
> superspeed controller (such as dwc3) when connected to a superspeed
> port. We cannot use ep0 packet size as 64, right ? 

Correct me if I'm wrong, but MaxPacket for SS ep0 is 2^9 = 512B.
I'm curious if dfu-util will manage to handle ep0 MaxPacket size up to
512B.
It not, then we shall be able to fallback to 64B.


> That's why
> hardcoding is bad ;-)
> 



-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group