[POWERPC] Add workaround for MPICs with broken register reads

Some versions of PWRficient 1682M have an interrupt controller in which
the first register in each pair for interrupt sources doesn't always
read with the right polarity/sense values.

To work around this, keep a software copy of the register instead.  Since
it's not modified from the mpic itself, it's a feasible solution.  Still,
keep it under a config option to avoid wasting memory on other platforms.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/Kconfig

@@ -137,6 +137,16 @@ config MPIC_U3_HT_IRQS
 	depends on PPC_MAPLE
 	default y
 
+config MPIC_BROKEN_REGREAD
+	bool
+	depends on MPIC
+	help
+	  This option enables a MPIC driver workaround for some chips
+	  that have a bug that causes some interrupt source information
+	  to not read back properly. It is safe to use on other chips as
+	  well, but enabling it uses about 8KB of memory to keep copies
+	  of the register contents in software.
+
 config IBMVIO
 	depends on PPC_PSERIES || PPC_ISERIES
 	bool

arch/powerpc/platforms/pasemi/Kconfig

@@ -5,6 +5,7 @@ config PPC_PASEMI
 	select MPIC
 	select PPC_UDBG_16550
 	select PPC_NATIVE
+	select MPIC_BROKEN_REGREAD
 	help
 	  This option enables support for PA Semi's PWRficient line
 	  of SoC processors, including PA6T-1682M

arch/powerpc/sysdev/mpic.c

@@ -228,8 +228,13 @@ static inline u32 _mpic_irq_read(struct mpic *mpic, unsigned int src_no, unsigne
 	unsigned int	isu = src_no >> mpic->isu_shift;
 	unsigned int	idx = src_no & mpic->isu_mask;
 
-	return _mpic_read(mpic->reg_type, &mpic->isus[isu],
-			  reg + (idx * MPIC_INFO(IRQ_STRIDE)));
+#ifdef CONFIG_MPIC_BROKEN_REGREAD
+	if (reg == 0)
+		return mpic->isu_reg0_shadow[idx];
+	else
+#endif
+		return _mpic_read(mpic->reg_type, &mpic->isus[isu],
+				  reg + (idx * MPIC_INFO(IRQ_STRIDE)));
 }
 
 static inline void _mpic_irq_write(struct mpic *mpic, unsigned int src_no,
@@ -240,6 +245,11 @@ static inline void _mpic_irq_write(struct mpic *mpic, unsigned int src_no,
 
 	_mpic_write(mpic->reg_type, &mpic->isus[isu],
 		    reg + (idx * MPIC_INFO(IRQ_STRIDE)), value);
+
+#ifdef CONFIG_MPIC_BROKEN_REGREAD
+	if (reg == 0)
+		mpic->isu_reg0_shadow[idx] = value;
+#endif
 }
 
 #define mpic_read(b,r)		_mpic_read(mpic->reg_type,&(b),(r))

include/asm-powerpc/mpic.h

@@ -306,6 +306,10 @@ struct mpic
 	unsigned long		*hwirq_bitmap;
 #endif
 
+#ifdef CONFIG_MPIC_BROKEN_REGREAD
+	u32			isu_reg0_shadow[MPIC_MAX_IRQ_SOURCES];
+#endif
+
 	/* link */
 	struct mpic		*next;