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Date: Tue, 14 Feb 2006 00:20:35 -0500
From: Ed Goforth <egoforth@gmail.com>
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To: linuxppc-embedded@ozlabs.org
Subject: 440gx GPIO
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I am struggling with a problem and I hope someone can give me some
pointers.  We have a custom board with a 440gx.  I need to drive GPIO11
low.  The best as I can tell from the docs, I need to set bit 11 of the
TCR to 1 and bit 11 of the OR to 0 to do this.  I'm using kernel
2.4.18-timesys-4.0

Here's what I've tried:

Prior to making an calls, the values of the registers are:
or      0x00101000
tcr     0x00101700
odr     0x00000000
ir      0xeffff820


(from ibm440gx.h)
#define PPC440GX_GPIO0_ADDR  0x0000000140000700


Attempt one: write the bit directly:

  volatile gpio_t *gpio;
  volatile u32 or_reg;

  gpio = (gpio_t *) ioremap_nocache(0x40000700,
                                    sizeof(gpio_t));

  or_reg = gpio->or;
  or_reg &= 0x00100000;
  gpio->or = or_reg;


Attempt two: use the accessor routine:
  extern int ibm_gpio_out(__u32 device, __u32 mask, __u32 data);

  rc = ibm_gpio_out(0, 0x00100000, 0);


With either approach, I can read the registers fine.  But as soon as I
either modify gpio->or or call ibm_gpio_out(), the board hangs hard.

Any hints would be greatly appreciated.  On-list replies are fine; I am
a subscriber.

Thanks,
Ed