At Wed, 7 Apr 2010 11:55:19 -0400 (EDT), Alan Stern wrote: > > On Wed, 7 Apr 2010, Greg KH wrote: > > > Yeah, I really don't want to have to change every driver in different > > ways just depending on if someone thinks it is going to need to run on > > this wierd hardware. > > It's not weird hardware, as far as I know. It's just a 64-bit system > with a 32-bit USB host controller. > > (And remember, while there are 64-bit EHCI controllers, there are not > any 64-bit OHCI or UHCI controllers. So whenever somebody plugs a > full-speed or low-speed device into a 64-bit machine, they will face > this problem. It's like the old problem of ISA devices that could > only do DMA to addresses in the first 16 MB of memory -- what the > original GFP_DMA flag was intended for.) > > > Alan, any objection to just using usb_buffer_alloc() for every driver? > > Or is that too much overhead? > > I don't know what the overhead is. But usb_buffer_alloc() requires the > caller to keep track of the buffer's DMA address, so it's not a simple > plug-in replacement. In addition, the consistent memory that > usb_buffer_alloc() provides is a scarce resource on some platforms. Yeah, also the area is aligned to kernel pages, and it may be much bigger than the requested (power-of-two). If not needed, we should avoid it. thanks, Takashi -- 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
