2009/2/3 David Vrabel <david.vrabel@xxxxxxx>: > Alan Stern wrote: > >>> The code that takes care of setting up the transfer buffer addresses >>>> should be split out and EXPORTed, because any HCD that supports sg will >>>> want to use it. >>> I'm not sure what code you're referring to? >> >> I'm talking about all this stuff, which (rightly) got left out of >> usb_sg_init_with_sg(): >> >> /* >> * Some systems need to revert to PIO when DMA is temporarily >> * unavailable. For their sakes, both transfer_buffer and >> * transfer_dma are set when possible. However this can only >> * work on systems without: >> [...] >> 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. > > For now, I would say that any HCD claiming sg-list support must always > support DMA. IMHO, the HCD claiming sg-list discussed just converts previous multiple URBs into one URB with multiple discontinuous transfer buffer in essence, so it is nothing with supporting DMA by HCD. Maybe Alan means DMA mapping, doesn't it? Thanks! > > It is unfortunate that neither myself nor Sarah can talk about the > specifics of the hardware where this sg list support is useful. > > David > -- > David Vrabel, Senior Software Engineer, Drivers > CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562 > Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/ > -- > 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 > -- Lei Ming -- 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
