Message-Id: <20230803173854.efdda6d30d88b85ee101ce6b@hugovil.com>
Date:   Thu, 3 Aug 2023 17:38:54 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        jirislaby@...nel.org, jringle@...dpoint.com,
        isaac.true@...onical.com, jesse.sung@...onical.com,
        tomasz.mon@...lingroup.com, l.perczak@...lintechnologies.com,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        stable@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Lech Perczak <lech.perczak@...lingroup.com>
Subject: Re: [RESEND PATCH v8 06/10] serial: sc16is7xx: fix regression with
 GPIO configuration

On Thu, 3 Aug 2023 14:10:30 -0600
Rob Herring <robh+dt@...nel.org> wrote:

> On Thu, Aug 3, 2023 at 11:54 AM Hugo Villeneuve <hugo@...ovil.com> wrote:
> >
> > On Mon, 31 Jul 2023 14:41:15 -0400
> > Hugo Villeneuve <hugo@...ovil.com> wrote:
> >
> > > On Mon, 31 Jul 2023 12:04:45 -0600
> > > Rob Herring <robh+dt@...nel.org> wrote:
> > >
> > > > On Mon, Jul 31, 2023 at 10:46 AM Hugo Villeneuve <hugo@...ovil.com> wrote:
> > > > >
> > > > > On Mon, 31 Jul 2023 09:31:53 -0600
> > > > > Rob Herring <robh+dt@...nel.org> wrote:
> > > > >
> > > > > > On Mon, Jul 24, 2023 at 9:54 AM Hugo Villeneuve <hugo@...ovil.com> wrote:
> > > > > > >
> > > > > > > On Sat, 22 Jul 2023 17:15:26 +0200
> > > > > > > Greg KH <gregkh@...uxfoundation.org> wrote:
> > > > > > >
> > > > > > > > On Sat, Jul 22, 2023 at 10:47:24AM -0400, Hugo Villeneuve wrote:
> > > > > > > > > On Fri, 21 Jul 2023 13:24:19 -0600
> > > > > > > > > Rob Herring <robh+dt@...nel.org> wrote:
> > > > > > > > >
> > > > > > > > > > On Fri, Jul 21, 2023 at 10:19 AM Hugo Villeneuve <hugo@...ovil.com> wrote:
> > > > > > > > > > >
> > > > > > > > > > > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > > > > > > > > > >
> > > > > > > > > > > Commit 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
> > > > > > > > > > > and commit 21144bab4f11 ("sc16is7xx: Handle modem status lines")
> > > > > > > > > > > changed the function of the GPIOs pins to act as modem control
> > > > > > > > > > > lines without any possibility of selecting GPIO function.
> > > > > > > > > >
> > > > > > > > > > Requiring a new DT property is not fixing a kernel regression. You
> > > > > > > > > > should be returning the kernel to original behavior and then have a
> > > > > > > > > > new DT property for new behavior.
> > > > > > > > >
> > > > > > > > > Hi Rob,
> > > > > > > > > please read the entire patch history starting from V1
> > > > > > > > >  and you will understand why this course of action was
> > > > > > > > >  not selected.
> > > > > > > >
> > > > > > > > That's not going to happen, sorry, you need to explain it here, in this
> > > > > > > > patch series, why a specific action is being taken over another one, as
> > > > > > > > no one has time to go dig through past history, sorry.
> > > > > > >
> > > > > > > Hi Rob,
> > > > > > > I initially submitted a patch to revert the kernel to original
> > > > > > > behavior, but it created more problems because the patch was
> > > > > > > unfortunately split in two separate patches, and mixed with other non
> > > > > > > closely-related changes. It was also noted to me that reverting to the
> > > > > > > old behavior would break things for some users.
> > > > > > >
> > > > > > > It was suggested to me by a more experienced kernel developer to
> > > > > > > "suggest a fix, instead of hurrying a revert":
> > > > > > >
> > > > > > >     https://lkml.org/lkml/2023/5/17/758
> > > > > >
> > > > > > Do I have to go read this to decipher the justification and reasoning?
> > > > > > When Greg says "in this patch series", he means in the commit messages
> > > > > > of the patches. You send v9 already and it doesn't have that. The
> > > > > > patchset needs to stand on its own summarizing any relevant prior
> > > > > > discussions.
> > > > > >
> > > > > > I never suggested doing a revert.
> > > > >
> > > > > Hi Rob,
> > > > > I am sorry, but this is exactly what I "deciphered" from your
> > > > > original email.
> > > > >
> > > > > I am trying very hard to understand exactly what you mean, but it is
> > > > > not that obvious for me. If something is not clear in my commit message,
> > > > > I will try to improve it. But before, let's try to focus on making sure
> > > > > I understand more clearly what you want exactly.
> > > > >
> > > > > > Obviously, someone still wants the
> > > > > > new feature.
> > > > >
> > > > > I assume that you refer to the "new feature" as what was added in
> > > > > the commit 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control
> > > > > lines")?
> > > >
> > > > Shrug. It's one of the 2 commits mentioned, I don't know which one
> > > > exactly. Whichever one changed default behavior from use GPIOs to use
> > > > modem ctrl lines.
> > > >
> > > > Reading it again, I *think* this patch is correct. Default behavior is
> > > > restored to use GPIOs. The DT property is needed to enable modem ctrl
> > > > lines.
> > >
> > > Hi,
> > > this is correct.
> > >
> > >
> > > > What's not okay is just saying, these platforms may or may not need an update:
> > > >
> > > >     arm64/boot/dts/freescale/fsl-ls1012a-frdm.dts
> > > >     mips/boot/dts/ingenic/cu1830-neo.dts
> > > >     mips/boot/dts/ingenic/cu1000-neo.dts
> > >
> > > Yes, my bad. I initially mentioned them and hoped to get some
> > > feedback, which I never got, and I kind of forgot about it.
> > >
> > > > You need to figure that out. Have you checked with maintainers of
> > > > these boards? When were they added and by who? At the same time or by
> > > > the same person would be a good indication the platform uses modem
> > > > ctrl lines. Or were these platforms in use before adding modem ctrl
> > > > support? Then they probably use GPIOs or nothing.
> > > >
> > > > If there are platforms which would regress if the modem ctrl feature
> > > > was just reverted, which ones are those?
> > >
> > > Ok, let me do some checks and get back to you on this.
> >
> > Hi Rob,
> > for this board:
> >     arm64/boot/dts/freescale/fsl-ls1012a-frdm.dts
> >
> > it uses a SC16IS740, which doesn't have any GPIOs nor modem
> > control lines, so no DT changes required.
> >
> > For these two Ingenic boards:
> >     mips/boot/dts/ingenic/cu1830-neo.dts
> >     mips/boot/dts/ingenic/cu1000-neo.dts
> >
> > They use a SC16IS752, which has shared modem control lines and GPIOs.
> > Unfortunately, the maintainers have not (yet) responded to my
> > inquiries. Also, I tried to search for schematics or block diagrams on
> > the net but couldn't find anything.
> >
> > These platforms were in use before the patch to add the modem control
> > lines was added. Then like you said they probably use these shared
> > lines as GPIOs or nothing, so no DT changes would be required.
> 
> Okay, that's useful (please add to the commit msg).

I added the information in the cover letter, but I can add it to the
actual patch commit message if you prefer.

> Still, what platform(s) need the modem control feature? Presumably
> that's whatever platform Lech and Tomasz work on. I guess given the
> Reviewed-by they are fine with needing a DT change.

Ok. I have previously also emailed Lech about that, but he has not
responded yet.

Thank you,
Hugo.

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