forked from Minki/linux
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>
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@ -917,12 +917,14 @@ static int bcm2835_pinconf_set(struct pinctrl_dev *pctldev,
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bcm2835_gpio_wr(pc, GPPUD, arg & 3);
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/*
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* Docs say to wait 150 cycles, but not of what. We assume a
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* 1 MHz clock here, which is pretty slow...
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* BCM2835 datasheet say to wait 150 cycles, but not of what.
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* But the VideoCore firmware delay for this operation
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* based nearly on the same amount of VPU cycles and this clock
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* runs at 250 MHz.
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*/
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udelay(150);
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udelay(1);
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bcm2835_gpio_wr(pc, GPPUDCLK0 + (off * 4), BIT(bit));
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udelay(150);
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udelay(1);
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bcm2835_gpio_wr(pc, GPPUDCLK0 + (off * 4), 0);
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} /* for each config */
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