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| author | Stefan Wahren <stefan.wahren@i2se.com> | 2016-10-31 13:21:33 +0000 |
|---|---|---|
| committer | Linus Walleij <linus.walleij@linaro.org> | 2016-11-04 16:28:28 +0100 |
| commit | b83bd893f3a04d35f5bfcf399c1034660e5b2403 (patch) | |
| tree | 39aed3d681977d8405e8bfc700c674a8b48290be | |
| parent | 684373eaa95fe6f85ef527281d87ff9ef07b084e (diff) | |
| download | op-kernel-dev-b83bd893f3a04d35f5bfcf399c1034660e5b2403.zip op-kernel-dev-b83bd893f3a04d35f5bfcf399c1034660e5b2403.tar.gz | |
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>
| -rw-r--r-- | drivers/pinctrl/bcm/pinctrl-bcm2835.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/pinctrl/bcm/pinctrl-bcm2835.c b/drivers/pinctrl/bcm/pinctrl-bcm2835.c index fa77165..b2dd278 100644 --- a/drivers/pinctrl/bcm/pinctrl-bcm2835.c +++ b/drivers/pinctrl/bcm/pinctrl-bcm2835.c @@ -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 */ |
