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. Best regards, Mirza -- 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
