Commit b83bd893 authored Oct 31, 2016 by Stefan Wahren Committed by Linus Walleij Nov 04, 2016

pinctrl: bcm2835: reduce GPPUD set-up time

Since the BCM2835 datasheet doesn't exactly specify the set-up time for
the GPIO Pull-up/down Clock Registers there was an assumption of 150 cycles
at a clock rate of 1 MHz. During a discussion [1] in the Raspberry Pi forum
it turns out that clock rate refers to the VPU which has a rate of 250 MHz.
So we can reduce the delay to a sensible value and update the comment above.

I tested this optimization with a Raspberry Pi B and a multimeter.

[1] - https://www.raspberrypi.org/forums/viewtopic.php?f=72&t=163352



Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

parent 684373ea

drivers/pinctrl/bcm/pinctrl-bcm2835.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -917,12 +917,14 @@ static int bcm2835_pinconf_set(struct pinctrl_dev *pctldev,

		bcm2835_gpio_wr(pc, GPPUD, arg & 3);
		/*
		* Docs say to wait 150 cycles, but not of what. We assume a
		* 1 MHz clock here, which is pretty slow...
		* BCM2835 datasheet say to wait 150 cycles, but not of what.
		* But the VideoCore firmware delay for this operation
		* based nearly on the same amount of VPU cycles and this clock
		* runs at 250 MHz.
		*/
		udelay(150);
		udelay(1);
		bcm2835_gpio_wr(pc, GPPUDCLK0 + (off * 4), BIT(bit));
		udelay(150);
		udelay(1);
		bcm2835_gpio_wr(pc, GPPUDCLK0 + (off * 4), 0);
		} /* for each config */