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authorStefan Wahren <stefan.wahren@i2se.com>2016-10-31 16:21:33 +0300
committerLinus Walleij <linus.walleij@linaro.org>2016-11-04 18:28:28 +0300
commitb83bd893f3a04d35f5bfcf399c1034660e5b2403 (patch)
tree39aed3d681977d8405e8bfc700c674a8b48290be /drivers/pinctrl/bcm
parent684373eaa95fe6f85ef527281d87ff9ef07b084e (diff)
downloadlinux-b83bd893f3a04d35f5bfcf399c1034660e5b2403.tar.xz
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>
Diffstat (limited to 'drivers/pinctrl/bcm')
-rw-r--r--drivers/pinctrl/bcm/pinctrl-bcm2835.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/pinctrl/bcm/pinctrl-bcm2835.c b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
index fa77165fab2c..b2dd278f18b1 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 */