On Wed, Dec 09, 2020 at 10:20:38AM +0100, Linus Walleij wrote: > On Mon, Dec 7, 2020 at 4:48 PM Johan Hovold <johan@xxxxxxxxxx> wrote: > > On Mon, Dec 07, 2020 at 03:34:23PM +0000, Marc Zyngier wrote: > > > > If they claim that their lines are available, and then refuse to > > > let the user play with it, that's just a bug willing to be fixed. > > > > My point was that this is how *all* gpio drivers work, and that muxing > > is somewhat orthogonal to the gpio controller implementation. > > This is true. It's because it is orthogonal that the separate subsystem > for pin control including pin muxing exists. > > Should I be really overly picky, the drivers that can mux lines like > this should be implementing the pin control mux driver side as > well just to make Linux aware of this. But if the muxing cannot > be changed by the kernel (albeit with special tools) then it would > be pretty overengineered for this case. Things would be much > easier if this wasn't some flashing configuration but more of a > runtime thing (which is kind of the implicit assumption in pin > control land). We'd still have problem of how to configure these hot-pluggable devices at runtime, so it's not necessarily easier. If I remember correctly the xr_serial driver under review is doing something like muxing at runtime, but by simply having whichever interface (tty or gpio) that claims the resource first implicitly set the mux configuration. I have to revisit that. > We don't really have many drivers that are "muxable by > (intrusive) flashing" as opposed to "muxable by setting some > bits" so in that way these FTDI drivers and siblings are special. Yeah, but the gpio-reserved-range (valid-mask) feature which Marc used comes close here. Johan
