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From: Johan Hovold <johan@kernel.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Johan Hovold <johan@kernel.org>, Marc Zyngier <maz@kernel.org>,
	linux-usb <linux-usb@vger.kernel.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	kernel-team@android.com
Subject: Re: [PATCH 0/4] USB: ftdio_sio: GPIO validity fixes
Date: Wed, 9 Dec 2020 16:42:21 +0100	[thread overview]
Message-ID: <X9DwXS2xaiOs033B@localhost> (raw)
In-Reply-To: <CACRpkdZ06vWY+mqR7bYd_WcEM6+N6v5GgTAYhr0p0KkNLa3Qnw@mail.gmail.com>

On Wed, Dec 09, 2020 at 10:20:38AM +0100, Linus Walleij wrote:
> On Mon, Dec 7, 2020 at 4:48 PM Johan Hovold <johan@kernel.org> wrote:
> > On Mon, Dec 07, 2020 at 03:34:23PM +0000, Marc Zyngier wrote:
> 
> > > If they claim that their lines are available, and then refuse to
> > > let the user play with it, that's just a bug willing to be fixed.
> >
> > My point was that this is how *all* gpio drivers work, and that muxing
> > is somewhat orthogonal to the gpio controller implementation.
> 
> This is true. It's because it is orthogonal that the separate subsystem
> for pin control including pin muxing exists.
> 
> Should I be really overly picky, the drivers that can mux lines like
> this should be implementing the pin control mux driver side as
> well just to make Linux aware of this. But if the muxing cannot
> be changed by the kernel (albeit with special tools) then it would
> be pretty overengineered for this case. Things would be much
> easier if this wasn't some flashing configuration but more of a
> runtime thing (which is kind of the implicit assumption in pin
> control land).

We'd still have problem of how to configure these hot-pluggable devices
at runtime, so it's not necessarily easier.

If I remember correctly the xr_serial driver under review is doing
something like muxing at runtime, but by simply having whichever
interface (tty or gpio) that claims the resource first implicitly set
the mux configuration. I have to revisit that.

> We don't really have many drivers that are "muxable by
> (intrusive) flashing" as opposed to "muxable by setting some
> bits" so in that way these FTDI drivers and siblings are special.

Yeah, but the gpio-reserved-range (valid-mask) feature which Marc used
comes close here.

Johan

      reply	other threads:[~2020-12-09 15:42 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04 16:47 Marc Zyngier
2020-12-04 16:47 ` [PATCH 1/4] gpiolib: cdev: Flag invalid GPIOs as used Marc Zyngier
2020-12-07 14:16   ` Johan Hovold
2020-12-07 14:59     ` Marc Zyngier
2020-12-09  9:25   ` Linus Walleij
2020-12-04 16:47 ` [PATCH 2/4] USB: serial: ftdi_sio: Report the valid GPIO lines to gpiolib Marc Zyngier
2020-12-09  9:28   ` Linus Walleij
2020-12-04 16:47 ` [PATCH 3/4] USB: serial: ftdi_sio: Log the CBUS GPIO validity Marc Zyngier
2020-12-07 14:29   ` Johan Hovold
2020-12-07 15:00     ` Marc Zyngier
2020-12-07 15:19       ` Johan Hovold
2020-12-09  9:35         ` Linus Walleij
2020-12-09 17:05           ` Johan Hovold
2020-12-09 17:39             ` Johan Hovold
2020-12-04 16:47 ` [PATCH 4/4] USB: serial: ftdi_sio: Drop GPIO line checking dead code Marc Zyngier
2020-12-07  9:55 ` [PATCH 0/4] USB: ftdio_sio: GPIO validity fixes Andy Shevchenko
2020-12-07 14:01 ` Johan Hovold
2020-12-07 14:41   ` Marc Zyngier
2020-12-07 15:08     ` Johan Hovold
2020-12-07 15:34       ` Marc Zyngier
2020-12-07 15:49         ` Johan Hovold
2020-12-09  9:20           ` Linus Walleij
2020-12-09 15:42             ` Johan Hovold [this message]

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