[RFC] musb: removing otg protocol support

[Bin Liu <b-liu@ti.com>]

On Mon, Mar 19, 2018 at 03:40:48PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Mar 19, 2018 at 09:20:23AM -0500, Bin Liu wrote:
> > On Sun, Mar 18, 2018 at 02:16:25PM +0100, Greg Kroah-Hartman wrote:
> > > On Fri, Mar 16, 2018 at 02:09:51PM -0500, Bin Liu wrote:
> > > > Hi,
> > > > 
> > > > The kernel usb stack and musb drivers have gone through some changes in
> > > > the past several kernel versions, such as adding otg fsm, musb runtime
> > > > PM, and musb otg state moving from musb to musb->xceiv... I am wondering
> > > > if the otg protocol (hnp, srp) functions are already broken in the musb
> > > > drivers, but I don't have a platform to confirm it.
> > > > 
> > > > Do we know by any chance there is still someone using the musb otg
> > > > functions in any relatively newer kernel and we still need to support
> > > > otg in musb?  If not, I am thinking to clean up the otg functions in
> > > > musb drivers to make the code easy to read and maintain.
> > > 
> > > By "clean up" do you mean "delete it"?  :)
> > 
> > Yes, delete it to make the driver state machine simpler and use less
> > flags for recording states.
> > 
> > > 
> > > I don't know of any real OTG hardware that ever shipped, does anyone
> > > else?
> > > 
> > > > If we can make the conclusion to remove it, I propose the patch below
> > > > to disable musb otg first, then clean up the driver later if nobody
> > > > complains about the otg function removal.
> > > 
> > > It will take years for people who make these types of devices to notice
> > > that OTG is removed, so be careful about this.  Refactor away, but
> > 
> > I personally think we can safely say there wasn't any true OTG products
> > where were under development in the last several years, but I am more
> > concerned if there was any such product released in the past, for
> > example omap24xx/34xx based, but was still actively maintained to the
> > latest kernel? Then deleting OTG protocol from musb drivers would break
> > them.
> 
> Wasn't the BeagleBone devices using that chipset?  If not, then you are

No, BeagleBone uses TI AM335x devices which have two MUSB controllers,
and released in around 2012. And I don't think anyone uses the true OTG
on AM335x, but omap24xx/34xx devices are much older which I don't know
the history...

> probably fine.

Sounds good. I will send a patch in a few weeks to disable OTG in musb
for v3.18-rc1, too late for v4.17 now I think...

Regards,
-Bin.
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