MIPS: Stop setting I6400 FTLBP

The FTLBP field in Config7 for the I6400 is intended as chicken bits for
debugging rather than as a field that software actually makes use of.
For best performance, FTLBP should be left at its default value of 0
with all TLB writes hitting the FTLB by default.

Additionally, since set_ftlb_enable is called from decode_configs before
decode_config4 which determines the size of the TLBs, this was
previously always setting FTLBP=3 for a 3:1 FTLB:VTLB write ratio which
makes abysmal use of the available FTLB resources.

This effectively reverts b0c4e1b79d8a ("MIPS: Set up FTLB probability
for I6400").

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Fixes: b0c4e1b79d8a ("MIPS: Set up FTLB probability for I6400")
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14021/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index def9d8d..7dd2dd4 100644 (file)
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -660,8 +660,6 @@
 
 #define MIPS_CONF7_IAR         (_ULCAST_(1) << 10)
 #define MIPS_CONF7_AR          (_ULCAST_(1) << 16)
-/* FTLB probability bits for R6 */
-#define MIPS_CONF7_FTLBP_SHIFT (18)
 
 /* WatchLo* register definitions */
 #define MIPS_WATCHLO_IRW       (_ULCAST_(0x7) << 0)

diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index a88d442..ae29050 100644 (file)
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -555,13 +555,8 @@ static int set_ftlb_enable(struct cpuinfo_mips *c, int enable)
                        write_c0_config6(config &  ~MIPS_CONF6_FTLBEN);
                break;
        case CPU_I6400:
-               /* I6400 & related cores use Config7 to configure FTLB */
-               config = read_c0_config7();
-               /* Clear the old probability value */
-               config &= ~(3 << MIPS_CONF7_FTLBP_SHIFT);
-               write_c0_config7(config | (calculate_ftlb_probability(c)
-                                          << MIPS_CONF7_FTLBP_SHIFT));
-               break;
+               /* There's no way to disable the FTLB */
+               return !enable;
        case CPU_LOONGSON3:
                /* Flush ITLB, DTLB, VTLB and FTLB */
                write_c0_diag(LOONGSON_DIAG_ITLB | LOONGSON_DIAG_DTLB |