On Tuesday 03 February 2009, Alan Stern wrote: > > > Ah, but you're forgetting the possibile cases in which the controller > > > doesn't support DMA. > > > > I don't think it's useful to speculate on possible hardware. If > > hardware like this is produced then we can revisit this. > > What do you mean? Of course hardware like this exists, and Linux > contains drivers for it. Otherwise there would be no reason for the > code to be written the way it is. Example, sl811hs is PIO-only. (Which reminds me, it's worth hooking up that CF card and making sure it didn't stop working since last time.) Not exactly the latest/hottest hardware, but significant to various users. And I tend to use musb_hdrc in PIO mode, thereby avoiding all the hassles associated with integration of the various random DMA engines, and when they need to fall back to PIO (or not). That's pretty much a daily thing; that IP is found in current mainstream embedded hardware from several vendors. Most vendors selling USB host controllers that don't try to conform to the PC-oriented standards (EHCI, OHCI, UHCI) will have a PIO mode, in addition to DMA support. And that PIO mode *will* be used in a variety of cases. - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
