[PPC440SPe] Convert machine check exceptions handling

Convert using fixup mechanism to suppressing MCK for the duration of config
read/write transaction: while fixups work fine with the case of a precise
exception, we identified a major drawback with this approach when there's
an imprecise case. In this scenario there is the following race condition:
the fixup is (by design) set to catch the instruction following the one
actually causing the exception; if an interrupt (e.g. decrementer) happens
between those two instructions, the ISR code is executed before the fixup
handler the machine check is no longer protected by the fixup handler as it
appears as within the ISR code. In consequence the fixup approach is being
phased out and replaced with explicit suppressing of MCK during a PCIe
config read/write cycle.

Signed-off-by: Grzegorz Bernacki <gjb@semihalf.com>

1 files changed, 0 insertions, 6 deletions

diff --git a/cpu/ppc4xx/traps.c b/cpu/ppc4xx/traps.c
index f5365cb..38b6f89 100644
--- a/cpu/ppc4xx/traps.c
+++ b/cpu/ppc4xx/traps.c
@@ -151,12 +151,6 @@ MachineCheckException(struct pt_regs *regs)
 	int uncorr_ecc = 0;
 #endif
 
-	/* Probing PCI(E) using config cycles may cause this exception
-	 * when a device is not present. To gracefully recover in such
-	 * scenarios config read/write routines need to be instrumented in
-	 * order to return via fixup handler. For examples refer to
-	 * pcie_in_8(), pcie_in_le16() and pcie_in_le32()
-	 */
 	if ((fixup = search_exception_table(regs->nip)) != 0) {
 		regs->nip = fixup;
 		val = mfspr(MCSR);