Re: [PATCH] sh: add resource of USB for SH7720

[Kristoffer Ericson <kristoffer.ericson@gmail.com>]

Anyone willing to give a quick explanation for usb-newbie :)

On Mon, 21 Jan 2008 16:05:53 +0900
Paul Mundt <lethal@linux-sh.org> wrote:

> On Mon, Jan 21, 2008 at 08:00:33AM +0100, Manuel Lauss wrote:
> > On Sun, Jan 20, 2008 at 01:15:16AM -0800, Kristoffer Ericson wrote:
> > > Greetings,
> > > 
> > > Without looking to heavily in the hd64465 datasheet, you think this
> > > would work for hd64465+SH7729 platform? It contains an OHCI based usb
> > > host.
> > 
> > Not without some additional changes to the OHCI stack.
> > The HD64465 OHCI (and the SH7760 OHCI too) can only do transfers
> > from/to its internal SRAM; the Linux OHCI stack simply assumes
> > that the HC can read all Transfer Descriptors (TD) and data
> > from main memory.
> > Also, SRAM is rather small (8kB IIRC) so you can forget about 
> > USB mass storage outright (and bluetooth dongles too), only
> > keyboards and mice work right.
> > Finally, the SRAM has different addresses, depending on who's
> > accessing it (HC or CPU), making it necessary to go over the
> > TDs and adjust the data pointers to 'HC-view' before transfer
> > and 'CPU-view' after they're done.
> > 
> > In short: the hardware sucks... ;-)
> > 
> http://marc.info/?l=linux-usb-devel&m\x120027668329758&w=2
> http://marc.info/?l=linux-usb-devel&m\x120055283608988&w=2