Re: [PATCH 1/3]USB: add Freescale high-speed USB SOC device controller driver

On Thursday 19 April 2007 7:53 pm, Li Yang-r58472 wrote:
> Hi Dave,
> 
> > -----Original Message-----
> > From: David Brownell [mailto:[email protected]]
> > Sent: Friday, April 20, 2007 2:24 AM
> > To: Li Yang-r58472
> > Cc: [email protected]; [email protected]; Schmid Bruce-R62923
> > Subject: Re: [PATCH 1/3]USB: add Freescale high-speed USB SOC device controller
> > driver
> > 
> > On Thursday 19 April 2007 2:53 am, Li Yang wrote:
> > > +static void *fsl_alloc_buffer(struct usb_ep *_ep, unsigned bytes,
> > > +               dma_addr_t *dma, gfp_t gfp_flags)
> > > +{...
> > > +}
> > 
> > You still need to fix this to use dma_alloc_coherent(), and its
> > sibling function to use dma_free_coherent().
> > 
> > This particular code assumes !CONFIG_NOT_COHERENT_CACHE ... which
> > ISTR you've said is not true on all the relevant PPC platforms, and
> > is certainly not true on the versions found (already?) in Freescale
> > ARM products.
> 
> This buffer is synced using dma_sync_single_*/dma_(un)map_single when
> the request is queued and when the transmission is complete.  To

No.  See <linux/usb_gadget.h> for the definition of usb_ep_alloc_buffer();
it says explicitly that such mapping calls are not required.

The only portable way to guarantee that is to allocate coherent memory.


> > > +               } else if ((setup->bRequestType & USB_RECIP_MASK)
> > > +                               == USB_RECIP_DEVICE) {
> > > +                       if (!udc->gadget.is_otg)
> > > +                               break;
> > > +                       else if (setup->bRequest ==
> > 						USB_DEVICE_B_HNP_ENABLE)
> > > +                               udc->gadget.b_hnp_enable = 1;
> > > + ...
> > 
> > And I'm curious about that stuff too ... should have asked before.
> > Is this a case where the hardware somehow snooping that request?
> 
> No, the hardware provide little assist on OTG.  We need to maintain
> the OTG states by software. 

That's the usual way:  software.


> > Because if it isn't, you're missing logic to poke some OTG register
> > when B_HNP_ENABLE is set ... nothing will happen when the device
> > suspends, no role switch or anything.
> 
> We have done the code for OTG, but it is not ready to be submitted
> for now.  So I decided not to include them in this patch. 

Well, you included _partial_ OTG support ... managing those flags
when is_otg is set (but nothing sets it yet).  :)

I guess it's just my taste that I'd include a comment right there
highlighting that this doesn't actually implement the OTG feature
it claims to implement ... but that's OK until something sets is_otg.

- Dave


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