Hi Lee,

On Tue, 31 Jan 2017, Lee Jones wrote:

On Tue, 31 Jan 2017, Peter Griffin wrote:

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On Tue, 31 Jan 2017, Lee Jones wrote:

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On Mon, 30 Jan 2017, Peter Griffin wrote:

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On Mon, 30 Jan 2017, Lee Jones wrote:

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On Mon, 30 Jan 2017, Peter Griffin wrote:

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On Mon, 30 Jan 2017, Lee Jones wrote:

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On Mon, 30 Jan 2017, Peter Griffin wrote:

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On Fri, 27 Jan 2017, Lee Jones wrote:

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On Wed, 25 Jan 2017, Peter Griffin wrote:

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On Tue, 24 Jan 2017, Lee Jones wrote:

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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 <redacted>
---
 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

[...]

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+		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.

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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 ;)

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[...]  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. ;)

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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.

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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>

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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.

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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.

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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.

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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.

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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'.

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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.

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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.

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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.