Hi Lee, On Mon, 30 Jan 2017, Lee Jones wrote: > On Mon, 30 Jan 2017, Peter Griffin wrote: > > On Mon, 30 Jan 2017, Lee Jones wrote: > > > On Mon, 30 Jan 2017, Peter Griffin wrote: > > > > On Fri, 27 Jan 2017, Lee Jones wrote: > > > > > On Wed, 25 Jan 2017, Peter Griffin wrote: > > > > > > On Tue, 24 Jan 2017, Lee Jones wrote: > > > > > > > > > > > > > There are now 2 possible separate/different Pinctrl states which can > > > > > > > be provided from platform data. One which encompasses the lines > > > > > > > required for HW flow-control (CTS/RTS) and another which does not > > > > > > > specify these lines, such that they can be used via GPIO mechanisms > > > > > > > for manually toggling (i.e. from a request by `stty`). > > > > > > > > > > > > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx> > > > > > > > --- > > > > > > > drivers/tty/serial/st-asc.c | 28 ++++++++++++++++++++++++++++ > > > > > > > 1 file changed, 28 insertions(+) > > > > > > > > > > > > > > diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c > > > > > > > index 397df50..03801ed 100644 > > > > > > > --- a/drivers/tty/serial/st-asc.c > > > > > > > +++ b/drivers/tty/serial/st-asc.c > > [...] > > > > > > > > + pinctrl_lookup_state(ascport->pinctrl, "manual-rts"); > > > > > > > + if (IS_ERR(ascport->states[MANUAL_RTS])) > > > > > > > + ascport->states[MANUAL_RTS] = NULL; > > > > > > > + > > > > > > > > > > > > The different pinctrl states looks like a neat solution to the problem. > > > > > > > > > > > > My only concern here is that 'default' state is implying a hw-flow-control > > > > > > pinmux config, and manual-rts is implying what is the current upstream > > > > > > 'default' pinmux config. > > > > > > > > > > > > Which maybe ok if you update all uarts, but currently only serial0 > > > > > > is updated. So the other uarts current 'default' is actually the same as serial0 > > > > > > 'manual-rts' grouping, which conceptually is odd. > > > > > > > > > > > > Would it not be better to make 'manual-rts' the default state? As that aligns > > > > > > to what is currently already the default for the other UARTS? And then make > > > > > > hw-flow-control the optional state for serial0? > > > > > > > > > > > > That also has the advantage that 'default' has the same meaning with older DT's. > > > > > > > > > > The reason it was done is this was because none of the other UARTs > > > > > require 2 separate Pinctrl configurations, only this one. Moreover, > > > > > if they support RTS/CTS then I believe that the lines should be > > > > > defined in Pinctrl. > > > > > > > > Yes I agree with that. > > > > > > > > > Thus, it was my plan to update all UART's default > > > > > Pinctrl configs to include the RTS/CTS lines. > > > > > > > > > > > > > I still don't see the point in changing the meaning of 'default' group and breaking > > > > ABI if you don't need to? > > > > > > > > As far as I can tell if you swap the meaning of 'default' and 'maunal-rts' > > > > groups you get all the benefits of this series whilst also maintaining backwards > > > > compatbility with older DT's. > > > > > > What makes you think this will break ABI? > > > > I've not tried it, but an older DT defines one group, 'default' which contains > > the same pin config as your new optional 'manual-rts' group. > > > > The driver now reads like the manual-rts pin config is optional and should be stored in > > ascport->states[MANUAL_RTS]. An older DT will pass that same pin config as the default > > group and it will be stored in ascport->states[DEFAULT]. > > > > That seems wrong to me, and if it executes OK it wouldn't be what you > > expect by reading the code. > > This makes no sense at a functional level. > > Old kernel, old DTB: > > ASC driver doesn't understand Pinctrl, but since only the "default" > state is defined, that's what will be used as a matter of course. > RTS/CTS aren't configured, but that doesn't matter because the DTS > does not advertise that HW flow-control is available. In this > use-case neither HW flow-control, nor manual toggling of the RTS line > is possible. > > New kernel, old DTB: > > ASC driver demands "default" and requests "manual-rts" Pinctrl states, > but "manual-rts" isn't available so "default" will be the only > utilised state. Unlike the first example above, "default" now > contains the RTS and CTS lines, No it doesn't, default just contains 'tx' & 'rx' pins, as it has always done until now. Which is IMO where the condusion arises, as it is the same pin configuration as what you are now calling 'manual-rts' which the driver just tried and failed to obtain (although in reality it has actually obtained those pins but stored them in DEFAULT instead. I presume this is why it didn't make sense to you above. >but since the DTS does not advertise > HW flow-control as available they will be harmlessly unused. This > configuration culminates in the same result as the first example > i.e. no HW flow-control and no manual toggling. However, there are no > detremental effects to the driver's functions. > <snip> >New kernel, new DTB: > > ASC driver demands "default" and requests "manual-rts" Pinctrl > states. If DTS advertises that HW flow-control is possible and the > client requests it, ASC will use the "default" state and HW > flow-control will commence. If HW flow-control is not requested by > the client and "manual-rts" is available, then ASC will request the > RTS line is handled by GPIO until such times as the client requests > HW flow-control, at which point ASC will disable GPIO and request the > "default" state again. Unless it is uart 1 or 2, in which case 'default' still only contains tx & rx pins, and you have the same situation as above. > > It is not possible to read C-code and make assumptions that the DTB > will be in a particular state as you suggest. > No disparity ever > exists and the code is always clear IMHO. > Really? ascport->states[DEFAULT]: may contain "tx, rx" or "tx, rx, cts & rts" ascport->states[MANUAL_RTS]: may contain "tx, rx", or it could be stored in DEFAULT And as the series currently is you have a mixture of the two in the same kernel depending on what instance of the UART you are. regards, Peter. -- 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
