[RFC] musb: removing otg protocol support

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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
probably fine.

thanks,

greg k-h
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