Hi Lee, On Tue, 31 Jan 2017, Lee Jones wrote: > On Tue, 31 Jan 2017, Peter Griffin wrote: > > On Tue, 31 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 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. > > > > > > I guess this is what happens when you try to explain semantics last > > > thing, after a long day at work. I chopped and changed the > > > descriptions and the ordering of these and it looks like some > > > peculiarities arose as a result. Let me try again with a fresh(ish) > > > mind. > > > > It is what happens when your semantics are overly complicated ;) > > > [...] and still understandable even late at night after a long day :) > > [0] > > It's not that I didn't understand the semantics. It's that I left the > wrong description in when cutting my text around. It's English I have > a problem with late at night, not understanding this simple concept. ;) > > > > 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. The RTS and CTS lines will not be present, but since > > > the DTB is not advertising HW flow-control as a possibility, the IP > > > will not try to use those lines anyway. [DEFAULT] will contain the > > > "default" state as proposed by the current DTB, so that is also > > > semantically correct. > > > > > > > >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. > > > > > > Doesn't matter. "default" is non-descriptive. I could understand an > > > argument were you to say that the "manual-rts" should not contain a > > > non-manual-rts state, but the "default" state should just contain > > > whatever the default configuration is, and in the case of UART 1 and > > > UART 2 the default state (until they are HW flow-control enabled -- > > > which I plan to do as a follow-up) is not to provide HW flow-control > > > pins. These semantics are unchanged since authorship of the driver. > > > > > > > > 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? > > > > > > Yes. > > > > > > > ascport->states[DEFAULT]: may contain "tx, rx" or "tx, rx, cts & rts" > > > > > > Correct. "DEFAULT" does not mean "HW flow-control only". It's > > > whatever the default is, so can correctly contain either state, > > > depending on what the default state of the DTB is. > > > > > > > ascport->states[MANUAL_RTS]: may contain "tx, rx", or it could be stored in DEFAULT > > > > > > The last part of this is reiterating your previous point, which I > > > just answered. The correct description would be; "may contain *only* > > > "tx, rx", allowing "rts" to be manually controlled OR, may not be > > > populated". In the latter case it would not be semantically incorrect > > > for DEFAULT to be either HW flow-control capable "tx, rx, rts, cts" or > > > not "tx, rx" -- whichever is the default of the supplied DTB. > > > > > > > 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. > > > > > > Again, doesn't matter, since it's the DTB that provides the default > > > state. So, back when it was authored, the default state was HW > > > flow-control disabled. And in a newer DTB (again, until I follow-up > > > with more changes), the defaults for UART 1 and UART 2 are HW > > > flow-control disabled. > > > > > > Your issue seems to be that you've assumed since we now provide the > > > possibility of a "manual-rts" state, then the "default" state should > > > *only* be HW flow-control capable, which is not the case. > > > > No my feedback was that it would be clearer & simpler to make manual-rts the > > 'default' state, and 'hw-flow-control' the optional state. > > Absolutely not. The use of "manual-rts" is the corner-case here and > is not normally required. See below. > The "default" state should normally be > populated with whatever pins are available i.e. all 4 pins (including > "rts, cts") if they are wired up and only 2 pins (just "tx, rx") if > they are not. Yep OK, I agree :) > The submission of "manual-rts" is only required if the > RTS pin is required for some other purpose e.g. resetting a uC on a > draughtboard. All UARTs the SoC have the same st-asc IP, which suffers from the same hw flow control limitation. Also all instances on the SoC have rts/cts pins, the only limitation is board wiring. So I can't see why would you ever *not* want to deploy this dynamic pin switching solution if rts/cts is wired up at board level now the facility exists? Also regarding the naming of the second pin group, 'manual-rts' seems like a bad name as a logical extension of this set is to also offer the same dynamic switching for the CTS line. Maybe a better name would be 'tx-rx-only' or 'no-rts-cts'. > > > > It's the > > > 'uart-has-rtscts' property which determines this *not* whether the > > > second state has been provided. > > > > Yep, which is why IMO it makes more sense for the optional pin group to be the hw > > flow control pins which are obtained if the uart-has-rtscts property is present. > > There would normally only be one pin group. Your method would insist > we always provided 2, which would be surplus to requirement. Yep OK, agree with your point. > > >It is not logical to make any > > > inference using solely the presence or absence of the "manual-rts" > > > state. > > > > My suggestion would mean 'default' continues to mean 'tx & rx' pins, and the presence > > of 'uart-has-rtscts' would mean the driver attempts to obtain a hw-flow-control > > pin group. > > > > In this setup > > > > ascport->states[DEFAULT]: always contains tx, rx > > ascport->states[HWFLOW]: always contains tx, rx, cts, rts or nothing > > I know what your suggestion would mean, and I think it's hacky. > "default" means default, whatever that may be. We should have to a) > provide one Pinctrl if only one is required (most cases) and b) make > assumptions based solely on the presence/absence of the > 'uart-has-rtscts' property and nothing else. > > There is nothing complicated about that. Yep OK, I agree. > > > and the presence or lack of rts-gpio controls manual RTS toggling. This seems > > simpler than your current semantics, and still understandable even late at night > > after a long day :) > > I don't think your method makes it simpler at all. I think it makes > illogical assumptions (there is no reason why "default" should mean > "HW flow-control is disabled") and forces us to over-complicate the DTB. Yep OK, I agree. > > For the second part, see [0] above. :) > regards, Peter. -- 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
