Hi Noralf. On Tue, Aug 07, 2018 at 06:40:29PM +0200, Noralf Trønnes wrote: > Hi Sam, > > Den 02.08.2018 21.45, skrev Sam Ravnborg: > >The pardata supports implement a simple bus for devices > >that are connected using a parallel bus driven by GPIOs. > >The is often used in combination with simple displays > >that is often seen in older embedded designs. > >There is a demand for this support also in the linux > >kernel for HW designs that uses these kind of displays. > > > >The pardata bus uses a platfrom_driver that when probed > >creates devices for all child nodes in the DT, > >which are then supposed to be handled by pardata_drivers. > > > >Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx> > >--- > > From a quick look at this I have these comments: > 1. There can only be one implementation of this bus, the gpio one. > There are SOC's with parallel bus hardware so you need to allow for > more implementations. > 2. The client shouldn't do the bus signaling. This should be hidden > behind read and write functions in pardata. > 3. I would also suggest you add an address bus instead of the RS pin > 4. I don't think reset belongs in the bus. It's a device thing. Excellent feedback - I will address this in v2. > 5. You can use gpiod_set_array_value() in the gpio implementation. > Some gpio drivers can set all gpios at once. Yes, it is already used. But only for DB0 to DB7 as there are timing constraings for the others. > > I made an attempt at implementing a bus like this a while back: > https://github.com/notro/fbdbi/tree/master/i80 Thanks, very helpfull. v2 will take a while as I plan to have something that actually works before posting next version. One open question. Miguel Ojeda mentioned that there is already a limited fbdev driver made on top of parport (part of auxdisplay). Is it the correct design to come up with a new bus or should this try to build on top of parport? I did not check in details if using parport is possible, but from a quick look it is doable. But then we use parport for something that it originally was not designed for and we drag with us a lot of extra functionality. So I like the slimmer pardata bus. Sam _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
