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

On Thursday 19 April 2007 8:56 pm, Li Yang-r58472 wrote:
> 
> > > > 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.
> 
> Then I can remove the dma_sync_single calls from ep_queue() and done()?

Not a good idea.  There are two ways that a DMA address gets
provided to the lower level code:  (a) coherent buffer allocation,
as above, and (b) mapping done by driver, and re-used.  The former
doesn't need dma_sync_single().  The latter does.



> > 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.
> 
> Is it ok that I indicate this in the patch comment?

Comment, please -- folk will mostly be reading the code, not the
patch comments.  Just a brief comment will suffice.

- Dave

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