X1000: remove bogus GPIO Z mutex

There's absolutely no way for gpio_config() to get called from two
different threads due to the co-operative threading model, and it
is unsafe to call from IRQ context no matter what we do.

Change-Id: I58f7d1f68c7a414610bb020e26b774cb1015a3b0

2 files changed, 4 insertions, 31 deletions

diff --git a/firmware/target/mips/ingenic_x1000/gpio-x1000.c b/firmware/target/mips/ingenic_x1000/gpio-x1000.c
index 8e93f865bf..40e4c5e631 100644
--- a/firmware/target/mips/ingenic_x1000/gpio-x1000.c
+++ b/firmware/target/mips/ingenic_x1000/gpio-x1000.c
@@ -22,16 +22,8 @@
 #include "gpio-x1000.h"
 #include "kernel.h"
 
-#ifndef BOOTLOADER_SPL
-struct mutex gpio_z_mutex;
-#endif
-
 void gpio_init(void)
 {
-#ifndef BOOTLOADER_SPL
-    mutex_init(&gpio_z_mutex);
-#endif
-
     /* Any GPIO pins left in an IRQ trigger state need to be switched off,
      * because the drivers won't be ready to handle the interrupts until they
      * get initialized later in the boot. */
@@ -44,20 +36,6 @@ void gpio_init(void)
     }
 }
 
-void gpio_lock(void)
-{
-#ifndef BOOTLOADER_SPL
-    mutex_lock(&gpio_z_mutex);
-#endif
-}
-
-void gpio_unlock(void)
-{
-#ifndef BOOTLOADER_SPL
-    mutex_unlock(&gpio_z_mutex);
-#endif
-}
-
 void gpio_config(int port, unsigned pinmask, int func)
 {
     unsigned intr = REG_GPIO_INT(port);
@@ -65,7 +43,6 @@ void gpio_config(int port, unsigned pinmask, int func)
     unsigned pat1 = REG_GPIO_PAT1(port);
     unsigned pat0 = REG_GPIO_PAT0(port);
 
-    gpio_lock();
     if(func & 8) jz_set(GPIO_INT(GPIO_Z), (intr & pinmask) ^ pinmask);
     else         jz_clr(GPIO_INT(GPIO_Z), (~intr & pinmask) ^ pinmask);
     if(func & 4) jz_set(GPIO_MSK(GPIO_Z), (mask & pinmask) ^ pinmask);
@@ -75,6 +52,5 @@ void gpio_config(int port, unsigned pinmask, int func)
     if(func & 1) jz_set(GPIO_PAT0(GPIO_Z), (pat0 & pinmask) ^ pinmask);
     else         jz_clr(GPIO_PAT0(GPIO_Z), (~pat0 & pinmask) ^ pinmask);
     REG_GPIO_Z_GID2LD = port;
-    gpio_unlock();
     gpio_set_pull(port, pinmask, func & 16);
 }
diff --git a/firmware/target/mips/ingenic_x1000/gpio-x1000.h b/firmware/target/mips/ingenic_x1000/gpio-x1000.h
index f1a65b37b5..cfbe86338a 100644
--- a/firmware/target/mips/ingenic_x1000/gpio-x1000.h
+++ b/firmware/target/mips/ingenic_x1000/gpio-x1000.h
@@ -26,12 +26,11 @@
  * --------
  *
  * To assign a new function to a GPIO, call gpio_config(). This uses the
- * hardware's GPIO Z facility to atomically most GPIO registers at once,
+ * hardware's GPIO Z facility to atomically set most GPIO registers at once,
  * so it can be used to make any state transition safely. Since GPIO Z is
- * protected by a mutex, you can't call gpio_config() from interrupt context.
- *
- * If you need to use GPIO Z directly, then use gpio_lock() and gpio_unlock()
- * to acquire the mutex.
+ * a global hardware resource, it is unsafe to call gpio_config() from IRQ
+ * context -- if the interrupted code was also running gpio_config(), then
+ * the results would be unpredictable.
  *
  * Depending on the current GPIO state, certain state transitions are safe to
  * perform without locking, as they only change one register:
@@ -74,8 +73,6 @@
 #define GPIO_IRQ_EDGE(i)    (0x1e|((i)&1))
 
 extern void gpio_init(void);
-extern void gpio_lock(void);
-extern void gpio_unlock(void);
 extern void gpio_config(int port, unsigned pinmask, int func);
 
 static inline void gpio_out_level(int port, unsigned pinmask, int level)