[U-Boot] [PATCH 2/4] usb: add 'bcm_udc_otg' support

[Marek Vasut <marex@denx.de>]

On Saturday, January 24, 2015 at 12:48:15 AM, Steve Rae wrote:
> On 15-01-21 11:05 PM, Marek Vasut wrote:
> > On Tuesday, January 20, 2015 at 11:42:08 PM, Steve Rae wrote:
> >> Implement the UDC support for the USB OTG interface.
> >> 
> >> Signed-off-by: Steve Rae <srae@broadcom.com>
> >> ---
> > 
> > General question -- this bcm controller you're adding here isn't by
> > any chance a DWC2 controller, or is it ? There's already a driver
> > for DWC2 in drivers/usb/gadget/s3c_udc_otg.c . This driver should really
> > be properly renamed though ;-/
> > 
> > If this is not DWC2, do you know what controller this is please ?
> 
> yes -- it is a DWC2....
> 
> So, I have had a quick look at the s3c_udc_otg*.c code....
> 
> First observation is that there is a completely different philosophy in
> the implementation. For example, the the interrupt handler routine(s),
> Broadcom is using #defines (sysmap.h which BTW are autogenerated by our
> Device Team) whereas "S3C" is using a "s3c_usbotg_reg" structure for the
> 'address' and #defines for the 'data/masks'. I'm not suggesting that one
> is better than the other, they are just different.

Hi!

The later is accepted by U-Boot as the preferred way, so the s3c is doing
things right.

> So, how do we proceed?

At this point, the Altera SoCFPGA and Samsung Exynos both use this s3c
driver to operate the DWC2 core in gadget mode. It should be trivial to
add support for the boardcom SoC, just follow the Altera example.

I would like to avoid situation where we have two drivers for a single
IP block.

> - is the ultimate goal to get to a proper gadget driver for DWC2? (I
> don't really know enough about this yet, so I apologize for these
> questions....)

Yes, but we already have one to my knowledge.

> - is the "S3C" code a proper 'gadget' driver and/or is it a better
> starting point to get to a gadget driver?

Yes, and it's thoroughly tested already.

> - I don't have enough time right now to really investigate the existing
> "S3C" and implement it on our board(s); they are significantly different
> and it looks like it will take a lot of effort - is there someone (Denx
> or community) that could assist me?

Sure, just start asking the questions.

> - Could we continue to review this patchset and accept it; then
> establish a team to provide a "DWC2 gadget" that could be used going
> forward?

No, unless there's a convincing technical argument that the currently
mainline DWC2 gadget driver (the s3c one) can absolutelly not be used
for the broadcom SoC, I want to avoid having two drivers for the same
IP core in mainline, sorry.

[...]

Sorry, at this point I have to push back a little.

Best regards,
Marek Vasut