On Wed, 2007-08-01 at 10:53 -0600, Matthew Wilcox wrote: > On Tue, Jul 31, 2007 at 09:18:08AM -0500, James Bottomley wrote: > > The other comment is that power saving seems to be a property of the > > transport rather than the host. If you do it in the transport classes, > > then you can expose all the knobs the actual transport possesses (which > > is, unfortunately, none for quite a few SCSI transports). > > Would it save any power to negotiate down to, say, FAST-20 for the SPI > transport? Or to negotiate narrow instead of wide, so fewer cables have > to be powered? Mechanically, I don't believe so. I'm not sure I can find any reports on it; however, I believe the power wastage SPI comes from the transcievers and terminators. There's the passive power from simply powering the resistive bus and then the RMS power from sending commands over an impedance circuit. simple physics on a 5v bus tells me that the former is likely to be far greater than the latter. Finally, if you think about what the bus is doing during signalling, the power drain is independent of the frequency so I think the faster you squirt your data, the lower the energy drain (hence high speed busses are actually lower energy than low speed ones if the number of bits you have to transfer remains constant). James - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
