RE: [PATCH 1/2] usb: dwc2: Option to disable dma descriptor mode

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> From: Felipe Balbi [mailto:balbi@xxxxxx]
> Sent: Tuesday, May 06, 2014 11:37 AM
> 
> On Tue, May 06, 2014 at 06:21:02PM +0000, Paul Zimmerman wrote:
> > > From: dinguyen@xxxxxxxxxx [mailto:dinguyen@xxxxxxxxxx]
> > > Sent: Monday, May 05, 2014 3:23 PM
> > >
> > > Even though the IP supports Descriptor DMA mode, it does not support SPLIT
> > > transactions in this mode. Since the driver can get the Descriptor DMA mode
> > > support from hardware, the driver in its currently form cannot fully support
> > > LS/FS devices connected to a HS Hub when Descriptor DMA mode is enabled in the
> > > driver. Thus, we give the option to disable Descriptor DMA from device tree.
> >
> > Hi Dinh,
> >
> > Instead of this patch, how about if we make the driver default to buffer
> > DMA mode instead, and if anyone wants to use descriptor DMA mode, they
> > can add a DT property for that? I don't think anyone will want that,
> > since as you say it doesn't fully support LS/FS devices in that mode.
> >
> > The driver originally worked like that. I guess the default got changed by
> > one of Matthijs' patches, and I didn't notice it.
> 
> if this is the case, I guess you could call it a regression - well, it
> _did_ break LS/FS use cases - and still merge it during the -rc cycle.

Well, the change from Matthijs went in on August 30th last year. So it's
not exactly a recent regression ;)

-- 
Paul

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