MIPS: Octeon: Apply CN63XXP1 errata workarounds.

The CN63XXP1 needs a couple of workarounds to ensure memory is not written
in unexpected ways.

All PREF with hints in the range 0-4,6-24 are replaced with PREF 28. We
pass a flag to the assembler to cover compiler generated code, and patch
uasm for the dynamically generated code.

The write buffer threshold is reduced to 4.

Signed-off-by: David Daney <[e-mail]>
Patchwork: http://patchwork.linux-mips.org/patch/1672/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/Makefile

···
 ifeq (,$(findstring march=octeon, $(cflags-$(CONFIG_CPU_CAVIUM_OCTEON))))
 cflags-$(CONFIG_CPU_CAVIUM_OCTEON) += -Wa,-march=octeon
 endif
+cflags-$(CONFIG_CAVIUM_CN63XXP1) += -Wa,-mfix-cn63xxp1
 
 cflags-$(CONFIG_CPU_R4000_WORKAROUNDS)	+= $(call cc-option,-mfix-r4000,)
 cflags-$(CONFIG_CPU_R4400_WORKAROUNDS)	+= $(call cc-option,-mfix-r4400,)

arch/mips/cavium-octeon/Kconfig

···
 	depends on CPU_CAVIUM_OCTEON
 	default "y"
 
+config CAVIUM_CN63XXP1
+	bool "Enable CN63XXP1 errata worarounds"
+	depends on CAVIUM_OCTEON_SPECIFIC_OPTIONS
+	default "n"
+	help
+	  The CN63XXP1 chip requires build time workarounds to
+	  function reliably, select this option to enable them.  These
+	  workarounds will cause a slight decrease in performance on
+	  non-CN63XXP1 hardware, so it is recommended to select "n"
+	  unless it is known the workarounds are needed.
+
 config CAVIUM_OCTEON_2ND_KERNEL
 	bool "Build the kernel to be used as a 2nd kernel on the same chip"
 	depends on CAVIUM_OCTEON_SPECIFIC_OPTIONS

arch/mips/cavium-octeon/setup.c

···
 	cvmmemctl.s.wbfltime = 0;
 	/* R/W If set, do not put Istream in the L2 cache. */
 	cvmmemctl.s.istrnol2 = 0;
-	/* R/W The write buffer threshold. */
-	cvmmemctl.s.wbthresh = 10;
+
+	/*
+	 * R/W The write buffer threshold. As per erratum Core-14752
+	 * for CN63XX, a sc/scd might fail if the write buffer is
+	 * full.  Lowering WBTHRESH greatly lowers the chances of the
+	 * write buffer ever being full and triggering the erratum.
+	 */
+	if (OCTEON_IS_MODEL(OCTEON_CN63XX_PASS1_X))
+		cvmmemctl.s.wbthresh = 4;
+	else
+		cvmmemctl.s.wbthresh = 10;
+
 	/* R/W If set, CVMSEG is available for loads/stores in
 	 * kernel/debug mode. */
 #if CONFIG_CAVIUM_OCTEON_CVMSEG_SIZE > 0
···
 	 * is max legal value. */
 	cvmmemctl.s.lmemsz = CONFIG_CAVIUM_OCTEON_CVMSEG_SIZE;
 
+	write_c0_cvmmemctl(cvmmemctl.u64);
 
 	if (smp_processor_id() == 0)
 		pr_notice("CVMSEG size: %d cache lines (%d bytes)\n",
 			  CONFIG_CAVIUM_OCTEON_CVMSEG_SIZE,
 			  CONFIG_CAVIUM_OCTEON_CVMSEG_SIZE * 128);
-
-	write_c0_cvmmemctl(cvmmemctl.u64);
 
 	/* Move the performance counter interrupts to IRQ 6 */
 	cvmctl = read_c0_cvmctl();
···
 
 void prom_free_prom_memory(void)
 {
+	if (OCTEON_IS_MODEL(OCTEON_CN63XX_PASS1_X)) {
+		/* Check for presence of Core-14449 fix.  */
+		u32 insn;
+		u32 *foo;
+
+		foo = &insn;
+
+		asm volatile("# before" : : : "memory");
+		prefetch(foo);
+		asm volatile(
+			".set push\n\t"
+			".set noreorder\n\t"
+			"bal 1f\n\t"
+			"nop\n"
+			"1:\tlw %0,-12($31)\n\t"
+			".set pop\n\t"
+			: "=r" (insn) : : "$31", "memory");
+
+		if ((insn >> 26) != 0x33)
+			panic("No PREF instruction at Core-14449 probe point.\n");
+
+		if (((insn >> 16) & 0x1f) != 28)
+			panic("Core-14449 WAR not in place (%04x).\n"
+			      "Please build kernel with proper options (CONFIG_CAVIUM_CN63XXP1).\n", insn);
+	}
 #ifdef CONFIG_CAVIUM_DECODE_RSL
 	cvmx_interrupt_rsl_enable();
 

arch/mips/mm/uasm.c

···
 I_u1u2u3(_mtc0)
 I_u2u1u3(_ori)
 I_u3u1u2(_or)
-I_u2s3u1(_pref)
 I_0(_rfe)
 I_u2s3u1(_sc)
 I_u2s3u1(_scd)
···
 I_u1(_syscall);
 I_u1u2s3(_bbit0);
 I_u1u2s3(_bbit1);
+
+#ifdef CONFIG_CPU_CAVIUM_OCTEON
+#include <asm/octeon/octeon.h>
+void __uasminit uasm_i_pref(u32 **buf, unsigned int a, signed int b,
+			    unsigned int c)
+{
+	if (OCTEON_IS_MODEL(OCTEON_CN63XX_PASS1_X) && a <= 24 && a != 5)
+		/*
+		 * As per erratum Core-14449, replace prefetches 0-4,
+		 * 6-24 with 'pref 28'.
+		 */
+		build_insn(buf, insn_pref, c, 28, b);
+	else
+		build_insn(buf, insn_pref, c, a, b);
+}
+UASM_EXPORT_SYMBOL(uasm_i_pref);
+#else
+I_u2s3u1(_pref)
+#endif
 
 /* Handle labels. */
 void __uasminit uasm_build_label(struct uasm_label **lab, u32 *addr, int lid)