sym scsi driver problem with 2.6.26 or newer debian kernel on p610 (fwd)

[Benjamin Herrenschmidt]

On Wed, 2009-06-24 at 07:57 +1000, Benjamin Herrenschmidt wrote:
> > I tried on a POWER3 box I have here "IBM,7044-170" and things work fine
> > here with current upstream. (I suspect a much smaller machine).
> > 
> > I will really need an actual bisection here... In the meantime, I'll see
> > if I can get my hand on one of these machines here.
> 
> Ok so I think we may have found it... looks like
> CONFIG_MPIC_BROKEN_REGREAD is what breaks it which is enabled by PA-Semi
> support in the .config.
> 
> Can you verify that disabling PA-Semi support removes that option from
> your .config and that once removed, it works again ?
> 
> We don't know yet -why- it breaks it, still investigating.

Do the following patch also fix it ?

Index: linux-work/arch/powerpc/sysdev/mpic.c
===================================================================
--- linux-work.orig/arch/powerpc/sysdev/mpic.c	2009-06-24 09:24:51.000000000 +1000
+++ linux-work/arch/powerpc/sysdev/mpic.c	2009-06-24 09:26:45.000000000 +1000
@@ -230,14 +230,16 @@ static inline u32 _mpic_irq_read(struct 
 {
 	unsigned int	isu = src_no >> mpic->isu_shift;
 	unsigned int	idx = src_no & mpic->isu_mask;
+	unsigned int	val;
 
+	val = _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
+		val = (val & (MPIC_VECPRI_MASK | MPIC_VECPRI_ACTIVITY)) |
+			mpic->isu_reg0_shadow[idx];
 #endif
-		return _mpic_read(mpic->reg_type, &mpic->isus[isu],
-				  reg + (idx * MPIC_INFO(IRQ_STRIDE)));
+	return val;
 }
 
 static inline void _mpic_irq_write(struct mpic *mpic, unsigned int src_no,
@@ -251,7 +253,8 @@ static inline void _mpic_irq_write(struc
 
 #ifdef CONFIG_MPIC_BROKEN_REGREAD
 	if (reg == 0)
-		mpic->isu_reg0_shadow[idx] = value;
+		mpic->isu_reg0_shadow[idx] =
+			value & ~(MPIC_VECPRI_MASK | MPIC_VECPRI_ACTIVITY);
 #endif
 }