On Tue, Mar 19, 2013 at 09:34:54AM +0800, Peter Chen wrote:
> On Mon, Mar 18, 2013 at 03:28:26PM +0100, Michael Grzeschik wrote:
> > On Fri, Mar 08, 2013 at 05:54:37PM +0200, Alexander Shishkin wrote:
> > > Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx> writes:
> > >
> > > > A static count of transfer descriptors was used everywhere in the driver
> > > > with the fixed number 4. This patch adds a define, named TD_COUNT, and
> > > > replaces all users of this value. This way its possible to have only one
> > > > parameter to change and limit the amount of tds per transfer.
> > >
> > > I think Svetoslav made exactly the same patch in his patchset, but I
> > > think this patchset will go first.
> >
> > I did not find any patch comparable by Svetoslav. But, that patch
> > is superseeded by that hunk in my current branch anyway, as every TD can
> > maintain five DMA buffers:
> >
> > diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
> > index 09bc6ea..c961e3b 100644
> > --- a/drivers/usb/chipidea/udc.c
> > +++ b/drivers/usb/chipidea/udc.c
> > @@ -688,8 +688,8 @@ static int _ep_queue(struct usb_ep *ep, struct usb_request *req)
> > goto done;
> > }
> >
> > - if (req->length > 4 * CI13XXX_PAGE_SIZE) {
> > - req->length = 4 * CI13XXX_PAGE_SIZE;
> > + if (req->length > 5 * CI13XXX_PAGE_SIZE) {
> > + req->length = 5 * CI13XXX_PAGE_SIZE;
> > retval = -EMSGSIZE;
> > dev_warn(mEp->ci->dev, "request length truncated\n");
> > }
>
> No, 4 is ok. There are 5 buffer Pointers are dTD, but the Buffer Point 0
> may not 4K aligned. Eg, if the reg->length is 18KB, and the buf DMA address
> is 1K aligned, it needs two dTDs.
> The first dTD only uses: 1KB, 4KB, 4KB, 4KB, 4KB as 5 buffers space.
When the first pointer is not aligned, then all other buffer pointers
will also not be. Because the payload will very likeley contiguous.
If the hardware limitation is to have 4K aligned buffer pointers in the
dma addresses, than this fix should be handled different than that.
So this limitation of 4 is a bogus workaround, and my attached hunk is
still valid.
Regards,
Michael
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