linux-kernel - Re: [RFC/PATCH] backlight: hx8357: prepare to conversion to gpiod API

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Message-ID: <Y0gICNqed+55mwuX@maple.lan>
Date:   Thu, 13 Oct 2022 13:43:52 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, Lee Jones <lee@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC/PATCH] backlight: hx8357: prepare to conversion to gpiod API

On Wed, Oct 12, 2022 at 01:34:38PM -0700, Dmitry Torokhov wrote:
> On Mon, Oct 10, 2022 at 10:36:00PM +0200, Linus Walleij wrote:
> > On Thu, Oct 6, 2022 at 12:05 PM Daniel Thompson
> > <daniel.thompson@...aro.org> wrote:
> > > On Thu, Oct 06, 2022 at 11:03:15AM +0200, Linus Walleij wrote:
> > > > On Tue, Oct 4, 2022 at 10:35 PM Dmitry Torokhov
> > > > <dmitry.torokhov@...il.com> wrote:
> > > >
> > > > > > Dmitry, could you fix this? Just patch away in gpiolib-of.c.
> > > > >
> > > > > Sure, I'll add a few quirks. I wonder what is the best way to merge
> > > > > this? I can create a bunch of IBs to be pulled, or I can send quirks to
> > > > > you/Bartosz and once they land send the patches to drivers...
> > > >
> > > > When I did it I was sufficiently convinced that I was the only one patching
> > > > the quirks in gpiolib-of.c that merge window so I just included it as
> > > > a hunk in the driver patch. If there will be some more patches to that
> > > > file I guess some separate patch(es) for gpiolib-of.c is needed, maybe
> > > > an immutable branch for those if it becomes a lot.
> > >
> > > Are renames likely to be a common quirk on the road to libgpiod
> > > conversion?
> > >
> > > I admit I sort of expected it to be common enough that there would be
> > > one rename quirk in the code supported by an alphabetized string table.
> > > Such a table would certainly still provoke troublesome merges but ones
> > > that are trivially resolved.
> >
> > Dmitry added a table of sorts, the problems are usually a bit unique
> > for each instance of nonstandard DT GPIO bindings, that's why I
> > mostly solved it with open coding in gpiolib-of.c.
>
> OK, so I sent out the patch adding "reset-gpios" -> "gpios-reset"
> translation quirk to keep compatibility with the legacy names, but
> we still need to figure out what to do with incorrect line polarity
> in current DTses in tree. Unlike with names we have no indication
> if out of tree DTSes specify correct polarity or not, so we can't
> reasonably come up with workarounds that are guaranteed to work for
> everyone. I see several options:
>
> 1 the driver could continue ignoring line polarity specified in DTS
>   (and use gpiod_set_value_raw()) and hope that they all/will be
>   wired in the same way?
>
> 2 we could fix up in-kernel DTSes, allow flexibility of connection
>   in new designs and respect polarity specified in out of tree DTSes,
>   but accept that there can be breakages with old DTSes not contributed
>   to the mainline or DTSes that were "cached" from an older kernel
>   release
>
> 3 add another quirk forcing "active low" polarity for the legacy
>   "gpios-reset" name, which will allow us respecting polarity in
>   new "reset-gpios" name.

I don't think they is any point in having a rename if legacy DTs break
anyway! Thus if there is a rename then there should also be an active low
quirk applied when the old name is used.


Daniel.