cpu/x86/mtrr: add helper for setting multiple MTRRs

Introduce concept of var_mtrr_context object for tracking and
assigning MTRR values. The algorithm is lifted from postcar_loader
code, but it's generalized for different type of users: setting
MSRs explicitly or deferring to a particular caller's desired
actions.

BUG=b:155426691,b:155322763

Change-Id: Ic03b4b617196f04071093bbba4cf28d23fa482d8
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41849
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

2 files changed, 98 insertions, 0 deletions

diff --git a/src/cpu/x86/mtrr/earlymtrr.c b/src/cpu/x86/mtrr/earlymtrr.c
index 5a2ce554fa..879b8eff27 100644
--- a/src/cpu/x86/mtrr/earlymtrr.c
+++ b/src/cpu/x86/mtrr/earlymtrr.c
@@ -65,3 +65,70 @@ void clear_all_var_mtrr(void)
 		wrmsr(MTRR_PHYS_BASE(i), mtrr);
 	}
 }
+
+void var_mtrr_context_init(struct var_mtrr_context *ctx, void *arg)
+{
+	ctx->upper_mask = (1U << (cpu_phys_address_size() - 32)) - 1;
+	ctx->max_var_mtrrs = get_var_mtrr_count();
+	ctx->used_var_mtrrs = 0;
+	ctx->arg = arg;
+}
+
+int var_mtrr_set_with_cb(struct var_mtrr_context *ctx, uintptr_t addr, size_t size,
+			int type, void (*callback)(const struct var_mtrr_context *ctx,
+						uintptr_t base_addr, size_t size,
+						msr_t base, msr_t mask))
+{
+	/* Utilize additional MTRRs if the specified size is greater than the
+	   base address alignment. */
+	while (size != 0) {
+		uint32_t addr_lsb;
+		uint32_t size_msb;
+		uint32_t mtrr_size;
+		msr_t base;
+		msr_t mask;
+
+		if (ctx->used_var_mtrrs >= ctx->max_var_mtrrs) {
+			printk(BIOS_ERR, "No more variable MTRRs: %d\n",
+					ctx->max_var_mtrrs);
+			return -1;
+		}
+
+		addr_lsb = fls(addr);
+		size_msb = fms(size);
+
+		/* All MTRR entries need to have their base aligned to the mask
+		   size. The maximum size is calculated by a function of the
+		   min base bit set and maximum size bit set. */
+		if (addr_lsb > size_msb)
+			mtrr_size = 1 << size_msb;
+		else
+			mtrr_size = 1 << addr_lsb;
+
+		base.hi = (uint64_t)addr >> 32;
+		base.lo = addr | type;
+		mask.hi = ctx->upper_mask;
+		mask.lo = ~(mtrr_size - 1) | MTRR_PHYS_MASK_VALID;
+		callback(ctx, addr, mtrr_size, base, mask);
+		ctx->used_var_mtrrs++;
+
+		size -= mtrr_size;
+		addr += mtrr_size;
+	}
+
+	return 0;
+}
+
+static void set_mtrr(const struct var_mtrr_context *ctx, uintptr_t base_addr, size_t size,
+			msr_t base, msr_t mask)
+{
+	int i = var_mtrr_context_current_mtrr(ctx);
+
+	wrmsr(MTRR_PHYS_BASE(i), base);
+	wrmsr(MTRR_PHYS_MASK(i), mask);
+}
+
+int var_mtrr_set(struct var_mtrr_context *ctx, uintptr_t addr, size_t size, int type)
+{
+	return var_mtrr_set_with_cb(ctx, addr, size, type, set_mtrr);
+}
diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index 301ea3052d..c1ee51accf 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -110,6 +110,37 @@ void clear_all_var_mtrr(void);
 
 asmlinkage void display_mtrrs(void);
 
+/* Variable MTRR structure to help track and set MTRRs prior to ramstage. This
+   and the following APIs can be used to set up more complex MTRR solutions
+   instead of open coding get_free_var_mtrr() and set_var_mtrr() or for determining
+   a future solution, such as postcar_loader. */
+struct var_mtrr_context {
+	uint32_t upper_mask;
+	int max_var_mtrrs;
+	int used_var_mtrrs;
+	void *arg; /* optional callback parameter */
+};
+
+/* Returns 0-relative MTRR from context. Use MTRR_PHYS_BASE|MASK macros for calculating
+   MSR address value. */
+static inline int var_mtrr_context_current_mtrr(const struct var_mtrr_context *ctx)
+{
+	return ctx->used_var_mtrrs;
+}
+
+/* Initialize var_mtrr_context object. Assumes all variable MTRRs are not yet used. */
+void var_mtrr_context_init(struct var_mtrr_context *ctx, void *arg);
+/* Allocate a variable mtrr base and mask, calling the provided callback for each MTRR
+   MSR base-mask pair needed to accommodate the address and size request.
+   Returns < 0 on error and 0 on success. */
+int var_mtrr_set_with_cb(struct var_mtrr_context *ctx,
+			uintptr_t addr, size_t size, int type,
+			void (*callback)(const struct var_mtrr_context *ctx,
+						uintptr_t base_addr, size_t size,
+						msr_t base, msr_t mask));
+/* Same as var_mtrr_set_with_cb() but just write the MSRs directly. */
+int var_mtrr_set(struct var_mtrr_context *ctx, uintptr_t addr, size_t size, int type);
+
 /*
  * Set the MTRRs using the data on the stack from setup_stack_and_mtrrs.
  * Return a new top_of_stack value which removes the setup_stack_and_mtrrs data.