Re: [OpenBIOS] [PATCH] ppc: use rfid when running under a CPU from the 970 family.

[Cédric Le Goater]

On 06/20/2016 09:39 AM, Alexander Graf wrote:
> On 20.06.16 09:34, Cédric Le Goater wrote:
> > A recent attempt to restrict the use of rfi to 64bit cpus in qemu
> > broke 32bit OpenBIOS when run under a 970.
> >
> > This is adding a dynamic check on the pvr to choose between rfi and
> > rfid. Only the 970 family is supported.
> > Signed-off-by: Cédric Le Goater
> >
> > Tested on qemu.
> >
> > arch/ppc/qemu/start.S |   25 +++++++++++++++++++++++--
> >  arch/ppc/start.S      |   25 +++++++++++++++++++++++--
> >  2 files changed, 46 insertions(+), 4 deletions(-)
> > Index: openbios.git/arch/ppc/qemu/start.S
> >
> > --- openbios.git.orig/arch/ppc/qemu/start.S
> > +++ openbios.git/arch/ppc/qemu/start.S
> > @@ -27,6 +27,27 @@
> >
> > #ifdef CONFIG_PPC_64BITSUPPORT
> >
> > +/* When running on ppc64, we cannot use rfi anymore. Let's try to
> > catch which cpu we are running on and act accordingly. This is
> > for 970s only.
>
> Do you think you could move the check into the cpu init function and use
> a global variable / live patching instead? I don't remember if we need
> to handle any faults before we reach that path.

I will try that. It would look better anyhow.

Thanks,

C.
> Alex
> > */
> >
> > +.macro do_rfi
> > mtsprg1	r3
> > mfpvr r3
> > rlwinm	r3,r3,16,16,31
> > cmplwi	cr1,r3,0x0039 	/* 970 CPUs */
> > beq- cr1,0f
> > cmplwi	cr1,r3,0x003C 	/* 970fx CPUs */
> > beq- cr1,0f
> > cmplwi	cr1,r3,0x0044 	/* 970mp CPUs */
> > beq- cr1,0f
> > mfsprg1	r3
> > rfi
> >
> > +0:
> > mfsprg1	r3
> > rfid
> >
> > +.endm
> >
> > /* We're trying to use the same code for the ppc32 and ppc64 handlers here.
> > On ppc32 we only save/restore the registers, C considers volatile.
> >
> > @@ -148,7 +169,7 @@
> >    ll	r31,(35 * ULONG_SIZE)(r1) ; \
> >  .endif ; \
> >    ll	r1,(1 * ULONG_SIZE)(r1) ;	/* restore stack at last */ \
> > rfi
> > do_rfi
> >
> > // PPC32
> >
> > @@ -319,7 +340,7 @@ VECTOR( 0x800, "FPU" ):
> >    ori	r3,r3,0x2000
> >    mtsrr1	r3
> >    mfsprg1	r3
> > RFI
> > do_rfi
> >
> > ILLEGAL_VECTOR( 0x900 )
> >  ILLEGAL_VECTOR( 0xa00 )
> > Index: openbios.git/arch/ppc/start.S
> > ===================================================================
> > --- openbios.git.orig/arch/ppc/start.S
> > +++ openbios.git/arch/ppc/start.S
> > @@ -25,6 +25,27 @@
> >  #define ILLEGAL_VECTOR( v )	.org __vectors + v ; bl trap_error ;
> >  #define VECTOR( v, dummystr )	.org __vectors + v ; vector__##v
> >
> > +/* When running on ppc64, we cannot use rfi anymore. Let's try to
> > catch which cpu we are running on and act accordingly. This is
> > for 970s only.
> > */
> >
> > +.macro do_rfi
> > mtsprg1	r3
> > mfpvr r3
> > rlwinm	r3,r3,16,16,31
> > cmplwi	cr1,r3,0x0039 	/* 970 CPUs */
> > beq- cr1,0f
> > cmplwi	cr1,r3,0x003C 	/* 970fx CPUs */
> > beq- cr1,0f
> > cmplwi	cr1,r3,0x0044 	/* 970mp CPUs */
> > beq- cr1,0f
> > mfsprg1	r3
> > rfi
> >
> > +0:
> > mfsprg1	r3
> > rfid
> >
> > +.endm
> >
> > #define EXCEPTION_PREAMBLE \
> >    mtsprg1	r1 ;		/* scratch */ \
> >    mfsprg0	r1 ;		/* exception stack in sprg0 */ \
> > @@ -252,7 +273,7 @@ exception_return:
> >    lwz	r11,44(r1)
> >    lwz	r12,48(r1)
> >    lwz	r1,4(r1)	// restore r1
> > rfi
> > do_rfi
> >
> > trap_error:
> >    mflr	r3
> > @@ -287,7 +308,7 @@ VECTOR( 0x800, "FPU" ):
> >    ori	r3,r3,0x2000
> >    mtsrr1	r3
> >    mfsprg1	r3
> > rfi
> > do_rfi
> >
> > ILLEGAL_VECTOR( 0x900 )
> >  ILLEGAL_VECTOR( 0xa00 )