On Mon, Jul 25, 2016 at 09:59:34PM +0200, Mirza Krak wrote: > 2016-07-25 16:15 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: > > On Mon, Jul 25, 2016 at 03:16:28PM +0200, Mirza Krak wrote: > >> 2016-07-25 13:30 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: > >> > > >> > I would've expected this to require some sort of infrastructure to allow > >> > devices connected to the GMI controller to acquire the bus via some API > >> > to select their chip. > >> > >> Yes, ultimately you would need some sort of infrastructure to allow > >> devices to acquire the GMI bus if you want to solve this in software. > >> But at the moment I do not see such an infrastructure in place, and is > >> it feasible to add one specifically for the GMI controller? If one > >> such infrastructure was in place we would need to modify all the > >> drivers that want to use to include Tegra specific infrastructure to > >> access the GMI bus? > >> > >> Since my knowledge is limited it hard for me to comment on this, maybe > >> there is a simple way of doing this? > > > > I don't think there's a simple way to do this. In order to properly > > implement it we'd need to implement a generic infrastructure for chip > > selects so that drivers such as the one for your CAN controller can be > > written without tying them specifically to the Tegra GMI controller. > > > > From what you and Jon were saying it sounds like the drivers are > > completely agnostic of any chip-select, so conversion won't be easy. > > But technically if these chips take a chip-select as input then it's > > always possible to hook them up to a controller that doesn't do this > > automatic translation of address to chip-select, so eventually some > > setup is bound to come along where they'd need explicit chip-select > > handling as well. > > > > I don't think it's fair to require you to implement this infrastructure > > if you don't actually need it. At the same time I want to be cautious > > and make sure we keep the driver and binding flexible enough to allow > > us to implement explicit chip-selects should we later need them. > > > > Thierry > > One thing that should be noted, and that is the GMI controller also > supports a DMA master mode (feature for the future?). > > I do not really know how this effects the binding we are discussing > but wanted to put it out there. Yes, that had occurred to me as well. I don't really have any good ideas on how to use that other than to implement it as a DMA engine driver and have drivers use those, if available. But I don't think we have to worry about it right now. If we ever need it, the binding can be extended in a backwards-compatible way. Thierry
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