arch/x86: introduce postcar stage/phase

Certain chipsets don't have a memory-mapped boot media
so their code execution for stages prior to DRAM initialization
is backed by SRAM or cache-as-ram. The postcar stage/phase
handles the cache-as-ram situation where in order to tear down
cache-as-ram one needs to be executing out of a backing
store that isn't transient. By current definition, cache-as-ram
is volatile and tearing it down leads to its contents disappearing.
Therefore provide a shim layer, postcar, that's loaded into
memory and executed which does 2 things:

1. Tears down cache-as-ram with a chipset helper function.
2. Loads and runs ramstage.

Because those 2 things are executed out of ram there's no issue
of the code's backing store while executing the code that
tears down cache-as-ram. The current implementation makes no
assumption regarding cacheability of the DRAM itself. If the
chipset code wishes to cache DRAM for loading of the postcar
stage/phase then it's also up to the chipset to handle any
coherency issues pertaining to cache-as-ram destruction.

Change-Id: Ia58efdadd0b48f20cfe7de2f49ab462306c3a19b
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14140
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

1 files changed, 115 insertions, 0 deletions

diff --git a/src/arch/x86/postcar_loader.c b/src/arch/x86/postcar_loader.c
new file mode 100644
index 000000000000..580cc4585c85
--- /dev/null
+++ b/src/arch/x86/postcar_loader.c
@@ -0,0 +1,115 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2016 Google Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <arch/cpu.h>
+#include <cbmem.h>
+#include <console/console.h>
+#include <cpu/x86/msr.h>
+#include <cpu/x86/mtrr.h>
+#include <program_loading.h>
+#include <rmodule.h>
+
+static inline void stack_push(struct postcar_frame *pcf, uint32_t val)
+{
+	uint32_t *ptr;
+
+	pcf->stack -= sizeof(val);
+	ptr = (void *)pcf->stack;
+	*ptr = val;
+}
+
+int postcar_frame_init(struct postcar_frame *pcf, size_t stack_size)
+{
+	void *stack;
+	msr_t msr;
+
+	msr = rdmsr(MTRR_CAP_MSR);
+
+	stack = cbmem_add(CBMEM_ID_ROMSTAGE_RAM_STACK, stack_size);
+	if (stack == NULL) {
+		printk(BIOS_ERR, "Couldn't add %zd byte stack in cbmem.\n",
+			stack_size);
+		return -1;
+	}
+
+	pcf->stack = (uintptr_t)stack;
+	pcf->stack += stack_size;
+
+	pcf->upper_mask = (1 << (cpu_phys_address_size() - 32)) - 1;
+
+	pcf->max_var_mttrs = msr.lo & MTRR_CAP_VCNT;
+
+	pcf->num_var_mttrs = 0;
+
+	return 0;
+}
+
+void postcar_frame_add_mtrr(struct postcar_frame *pcf,
+				uintptr_t addr, size_t size, int type)
+{
+	size_t align;
+
+	if (pcf->num_var_mttrs >= pcf->max_var_mttrs) {
+		printk(BIOS_ERR, "No more variable MTRRs: %d\n",
+			pcf->max_var_mttrs);
+		return;
+	}
+
+	/* Determine address alignment by lowest bit set in address. */
+	align = addr & (addr ^ (addr - 1));
+
+	if (align < size) {
+		printk(BIOS_ERR, "Address (%lx) alignment (%zx) < size (%zx)\n",
+			addr, align, size);
+		size = align;
+	}
+
+	/* Push MTRR mask then base -- upper 32-bits then lower 32-bits. */
+	stack_push(pcf, pcf->upper_mask);
+	stack_push(pcf, ~(size - 1) | MTRR_PHYS_MASK_VALID);
+	stack_push(pcf, 0);
+	stack_push(pcf, addr | type);
+	pcf->num_var_mttrs++;
+}
+
+void run_postcar_phase(struct postcar_frame *pcf)
+{
+	struct prog prog =
+		PROG_INIT(PROG_UNKNOWN, CONFIG_CBFS_PREFIX "/postcar");
+	struct rmod_stage_load rsl = {
+		.cbmem_id = CBMEM_ID_AFTER_CAR,
+		.prog = &prog,
+	};
+
+	/*
+	 * Place the number of used variable MTRRs on stack then max number
+	 * of variable MTRRs supported in the system.
+	 */
+	stack_push(pcf, pcf->num_var_mttrs);
+	stack_push(pcf, pcf->max_var_mttrs);
+
+	if (prog_locate(&prog))
+		die("Failed to locate after CAR program.\n");
+	if (rmodule_stage_load(&rsl))
+		die("Failed to load after CAR program.\n");
+
+	/* Set the stack pointer within parameters of the program loaded. */
+	if (rsl.params == NULL)
+		die("No parameters found in after CAR program.\n");
+
+	*(uintptr_t *)rsl.params = pcf->stack;
+
+	prog_run(&prog);
+}