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

[Steve Rae <srae@broadcom.com>]

On 15-01-24 03:47 AM, Marek Vasut wrote:
> 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.
OK -- Thanks for this information....
Steve
>
> Best regards,
> Marek Vasut
>