gpio: mpc8xxx: Do not reverse bits using bgpio

The MPC8xxx driver is always instantiating its generic GPIO functions
with the flag BGPIOF_BIG_ENDIAN. This means "big-endian bit order"
and means the bits representing the GPIO lines in the registers are
reversed around 31 bits so line 0 is at bit 31 and so forth down to
line 31 in bit 0.

Instead of looping into the generic MMIO gpio to do the simple
calculation of a bitmask, through a vtable call with two parameters
likely using stack frames etc (unless the compiler optimize it)
and obscuring the view for the programmer, let's just open-code
what the call does. This likely executes faster, saves space and
makes the code easier to read.

Cc: Liu Gang <[e-mail]>
Cc: Uwe Kleine-König <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-mpc8xxx.c

···
 #include <linux/slab.h>
 #include <linux/irq.h>
 #include <linux/gpio/driver.h>
+#include <linux/bitops.h>
 
 #define MPC8XXX_GPIO_PINS	32
 
···
 	unsigned int irqn;
 };
 
+/*
+ * This hardware has a big endian bit assignment such that GPIO line 0 is
+ * connected to bit 31, line 1 to bit 30 ... line 31 to bit 0.
+ * This inline helper give the right bitmask for a certain line.
+ */
+static inline u32 mpc_pin2mask(unsigned int offset)
+{
+	return BIT(31 - offset);
+}
+
 /* Workaround GPIO 1 errata on MPC8572/MPC8536. The status of GPIOs
  * defined as output cannot be determined by reading GPDAT register,
  * so we use shadow data register instead. The status of input pins
···
 	val = gc->read_reg(mpc8xxx_gc->regs + GPIO_DAT) & ~out_mask;
 	out_shadow = gc->bgpio_data & out_mask;
 
-	return !!((val | out_shadow) & gc->pin2mask(gc, gpio));
+	return !!((val | out_shadow) & mpc_pin2mask(gpio));
 }
 
 static int mpc5121_gpio_dir_out(struct gpio_chip *gc,
···
 
 	gc->write_reg(mpc8xxx_gc->regs + GPIO_IMR,
 		gc->read_reg(mpc8xxx_gc->regs + GPIO_IMR)
-		| gc->pin2mask(gc, irqd_to_hwirq(d)));
+		| mpc_pin2mask(irqd_to_hwirq(d)));
 
 	raw_spin_unlock_irqrestore(&mpc8xxx_gc->lock, flags);
 }
···
 
 	gc->write_reg(mpc8xxx_gc->regs + GPIO_IMR,
 		gc->read_reg(mpc8xxx_gc->regs + GPIO_IMR)
-		& ~(gc->pin2mask(gc, irqd_to_hwirq(d))));
+		& ~mpc_pin2mask(irqd_to_hwirq(d)));
 
 	raw_spin_unlock_irqrestore(&mpc8xxx_gc->lock, flags);
 }
···
 	struct gpio_chip *gc = &mpc8xxx_gc->gc;
 
 	gc->write_reg(mpc8xxx_gc->regs + GPIO_IER,
-		      gc->pin2mask(gc, irqd_to_hwirq(d)));
+		      mpc_pin2mask(irqd_to_hwirq(d)));
 }
 
 static int mpc8xxx_irq_set_type(struct irq_data *d, unsigned int flow_type)
···
 		raw_spin_lock_irqsave(&mpc8xxx_gc->lock, flags);
 		gc->write_reg(mpc8xxx_gc->regs + GPIO_ICR,
 			gc->read_reg(mpc8xxx_gc->regs + GPIO_ICR)
-			| gc->pin2mask(gc, irqd_to_hwirq(d)));
+			| mpc_pin2mask(irqd_to_hwirq(d)));
 		raw_spin_unlock_irqrestore(&mpc8xxx_gc->lock, flags);
 		break;
 
···
 		raw_spin_lock_irqsave(&mpc8xxx_gc->lock, flags);
 		gc->write_reg(mpc8xxx_gc->regs + GPIO_ICR,
 			gc->read_reg(mpc8xxx_gc->regs + GPIO_ICR)
-			& ~(gc->pin2mask(gc, irqd_to_hwirq(d))));
+			& ~mpc_pin2mask(irqd_to_hwirq(d)));
 		raw_spin_unlock_irqrestore(&mpc8xxx_gc->lock, flags);
 		break;