From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 2/5] ARM: bcm2835: Replace alt0/i2s_alt[02] with standard groups.
Date: Thu, 3 Mar 2016 14:26:12 -0700 [thread overview]
Message-ID: <56D8ABF4.6060801@wwwdotorg.org> (raw)
In-Reply-To: <1456510756-15337-3-git-send-email-eric@anholt.net>
On 02/26/2016 11:19 AM, Eric Anholt wrote:
> Since all of these pins were documented, we can use their names to
> explain what's going on.
> diff --git a/arch/arm/boot/dts/bcm2835-rpi-a-plus.dts b/arch/arm/boot/dts/bcm2835-rpi-a-plus.dts
> &gpio {
> + pinctrl-0 = <&i2c0_gpio0
> + &i2c1_gpio2
> + &gpclk0_gpio4
> + &gpclk1_gpio5
> + &spi0_gpio7
> + &pcm_gpio18
> + &pwm0_gpio40
> + &pwm1_gpio45
> + &gpioout
> + &alt3>;
> };
Why not convert alt3 to the new scheme too?
I think this configures too many pins, which in turn makes assumptions
about what those pins are used for that may not be valid.
Recent RPi firmware configures almost all expansion connector GPIOs as
GPIO-in. This ensures that no matter what is connected to the expansion
connector, there can be no signal conflicts due to both the bcm283x and
some external device both attempting to drive the same pin. I believe
the default Linux pinmux should adopt the same approach, by simply not
configuring any expansion connector pins except those known to have a
100% hard-coded usage. For example, the HAT I2C pins must only be used
for that purpose on the RPi, so even if the HW supported using them as
arbitrary GPIO or PWM or ..., we know they're actually I2C.
So, I think this list should only include configuration for pins
connected to on-board devices, or expansion pins that have a 100% known
purpose.
(I can't quite remember how many pins are being configured in the
upstream kernel's DT files at present; it's possible the complying with
this rule may involve removing some pinctrl settings that are currently
present to avoid conflicts. User-specific additions should come from DT
overlays or manual DT edits.)
next prev parent reply other threads:[~2016-03-03 21:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1456510756-15337-1-git-send-email-eric@anholt.net>
[not found] ` <1456510756-15337-2-git-send-email-eric@anholt.net>
2016-03-03 21:20 ` [PATCH 1/5] ARM: bcm2835: Define standard pinctrl groups in the gpio node Stephen Warren
2016-03-03 22:23 ` Eric Anholt
2016-03-03 22:32 ` Stephen Warren
2016-03-04 9:27 ` Martin Sperl
[not found] ` <1456510756-15337-3-git-send-email-eric@anholt.net>
2016-03-03 21:26 ` Stephen Warren [this message]
2016-03-03 22:28 ` [PATCH 2/5] ARM: bcm2835: Replace alt0/i2s_alt[02] with standard groups Eric Anholt
2016-03-03 22:34 ` Stephen Warren
2016-03-08 8:24 ` Linus Walleij
2016-03-08 16:42 ` Stephen Warren
[not found] ` <1456510756-15337-6-git-send-email-eric@anholt.net>
2016-03-08 8:25 ` [PATCH 5/5] ARM: bcm2835: Move most RPi default pin groups to their devices Linus Walleij
[not found] <1456266111-2508-1-git-send-email-eric@anholt.net>
2016-02-23 22:21 ` [PATCH 2/5] ARM: bcm2835: Replace alt0/i2s_alt[02] with standard groups Eric Anholt
2016-02-24 17:11 ` Stephen Warren
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