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

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

Hi Marek,

> 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.

Maybe it is a highest time to think about renaming s3c_* to dwc2_* and
avoid further confusion.

> 
> [...]
> 
> Sorry, at this point I have to push back a little.
> 
> Best regards,
> Marek Vasut



-- 
Best regards,

Lukasz Majewski

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