From 7f177a52a13e3d3751b599ae2b46d3d4658985cd Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Mon, 23 Sep 2013 14:01:53 +0100 Subject: [PATCH] MIPS: Tell R4k SC and MC variations apart There is no reliable way to tell R4000/R4400 SC and MC variations apart, however simple heuristic should give good results. Only the MC version supports coherent caching so we can rely on such a mode having been set for KSEG0 by the power-on firmware to reliably indicate an MC processor. SC processors reportedly hang on coherent cached memory accesses and Linux is linked to a cached load address so the firmware has to use the correct caching mode to download the kernel image in a cached mode successfully. OTOH if the firmware chooses to use either the non-coherent cached or the uncached mode for KSEG0 on an MC processor, then the SC variant will be reported, just as we currently do, so no regression here. Signed-off-by: Maciej W. Rozycki Cc: Jonas Gorski Cc: MIPS Mailing List Patchwork: https://patchwork.linux-mips.org/patch/5882/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/cpu-probe.c | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c index 5465dc1..040b83d 100644 --- a/arch/mips/kernel/cpu-probe.c +++ b/arch/mips/kernel/cpu-probe.c @@ -376,13 +376,33 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu) __cpu_name[cpu] = "R4000PC"; } } else { + int cca = read_c0_config() & CONF_CM_CMASK; + int mc; + + /* + * SC and MC versions can't be reliably told apart, + * but only the latter support coherent caching + * modes so assume the firmware has set the KSEG0 + * coherency attribute reasonably (if uncached, we + * assume SC). + */ + switch (cca) { + case CONF_CM_CACHABLE_CE: + case CONF_CM_CACHABLE_COW: + case CONF_CM_CACHABLE_CUW: + mc = 1; + break; + default: + mc = 0; + break; + } if ((c->processor_id & PRID_REV_MASK) >= PRID_REV_R4400) { - c->cputype = CPU_R4400SC; - __cpu_name[cpu] = "R4400SC"; + c->cputype = mc ? CPU_R4400MC : CPU_R4400SC; + __cpu_name[cpu] = mc ? "R4400MC" : "R4400SC"; } else { - c->cputype = CPU_R4000SC; - __cpu_name[cpu] = "R4000SC"; + c->cputype = mc ? CPU_R4000MC : CPU_R4000SC; + __cpu_name[cpu] = mc ? "R4000MC" : "R4000SC"; } } -- 2.7.4