On Mon, Aug 22, 2016 at 7:37 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Wednesday, August 17, 2016 8:14:42 PM CEST Rob Herring wrote: >> >> Before I spend more time on this, I'm looking mainly for feedback on the >> general direction and structure (the interface with the existing serial >> drivers in particular). > > Aside from the things that have already been mentioned in the discussion, > I wonder how this should relate to the drivers/input/serio framework. As I mentioned, I did investigate that route. > My impression is that there is some overlap in what you want > to do here, and what serio does today as a line discipline on top > of a tty line discipline (and on top of other non-uart serial > connections), so we should look into whether the two can be unified > or not. Here is what I found so far: > > For all I can tell, serio is only used for drivers/input/ but could > easily be extended to other subsystems. It currently uses its own > binary ID matching between drivers and devices through user space > interfaces, though adding a DT binding for it would appear to be > a good idea regardless. > > It also has a bus_type already, and with some operations defined on > it. In particular, it has an "interrupt" method that is used to > notify the client driver when a byte is available (and pass > that byte along with it). This seems to be a useful addition to > what you have. Since it is based on sending single characters > both ways, transferring large amounts of data would be slower, > but the interface is somewhat simpler. In principle, both > character based and buffer based interfaces could coexist here > as they do in some other interfaces (e.g. smbus). Given that about the only things it really provided are the bus_type and associated boilerplate without much of a client interface, it seemed to me that creating a new subsystem first made more sense. Then we can convert serio to use the new subsystem. I agree we'll probably need a character at time interface, but for initial targets a buffer based interface is what's needed. > While serio is typically layered on top of tty-ldisc (on top of > tty_port, which is often on top of uart_port) or on top of > i8042/ps2 drivers, I suppose we could add another back-end on top > of uart_port directly to avoid the ldisc configuration in many > cases when using devicetree based setup. This should also address > the main concern that Alan raised about generality of the > subsystem: we'd always leave the option of either manual configuration > of the tty-ldisc (for any tty_port) or configuring on-chip devices > (using uart_port) directly through DT. Of course the same thing > can be done if we hook into tty_port rather than uart_port. There are also some uart drivers that register directly with serio. I'm also thinking of using an ldisc backend as well as a way to move forward with the slave drivers while tty_port rework is being done. Of course that doesn't solve the fundamental problems with using an ldisc already. Going the tty_port route is going take some time to restructure things in the tty layer and require tree wide changes to tty drivers. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
