2016-07-25 15:39 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: > On Mon, Jul 25, 2016 at 03:30:34PM +0200, Mirza Krak wrote: >> 2016-07-25 13:59 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: >> > On Thu, Jul 21, 2016 at 10:56:44AM +0100, Jon Hunter wrote: >> >> >> > >> >> > +Note that the NOR controller does not have any internal chip-select address >> >> > +decoding and if you want to access multiple devices external chip-select >> >> > +decoding must be provided. >> >> >> >> Although it is true, you do have the MIO address space and so you could >> >> support two devices via the SNOR address space and MIO address space >> >> (assuming that the MIO can be used for the 2nd device). >> > >> > Now I'm even more confused. If the GMI controller itself can't select a >> > chip, what is the SNOR_SEL field in the SNOR_CONFIG_0 register for? Does >> > that not select a specific chip? >> > >> >> Furthermore, if you do have external logic to support multiple devices >> >> this would assume that the devices use the same timing and so are >> >> probably the same type. It also assumes both can fit in the 256MB >> >> address range. May be worth mentioning. >> > >> > Similarly if you switch between different devices, wouldn't you have to >> > reprogram the timing registers if they are different? >> > >> > The way I remember this kind of interface to work (it's been a long time >> > since I used one) is that in order to operate on a chip you need to >> > acquire the bus first. Typically that would be an API exposed by the bus >> > driver or some framework that the bus driver registers with. That API >> > arbitrates between multiple devices on the bus and makes sure that the >> > proper chip select is asserted and timing is programmed when you're >> > granted access. A driver that has acquired the bus can then perform what >> > operations they need and release the bus when done. >> > >> > SPI uses a mechanism like this, for example. >> > >> > Thierry >> >> From my experience (maybe not as long as yours :)) but these kind of >> things would be handled by the controller. At least with previous SOCs >> that I have used, PXA270, PXA300 and i.MX SOCs. >> >> That it has an address range per chip-select PIN and timing registers >> per chip-select. And thus eliminating a need for a infrastructure or >> framework. > > Okay, so the controllers have a translation table that needs to be > programmed and which maps address ranges to chip-selects. That's a nifty > feature, but I think it's also fairly specialized. In such a setup there > doesn't need to be a concept of chip-selects in software because it's > all transparently handled by the controller. Effectively the only time a > chip-select is needed is during the initial programming of the > controller when the translation table is set up. Yes, and in some cases you can not "program" the map as it is fixed in hardware. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
