i945: Enable changing VRAM size

On i945 the vram size is the default 8mb. It is also possible
to set it 1mb or 0mb hardcoding the GGC register in early_init.c

The intel documentation on i945, "Mobile Intel® 945 Express Chipset
Family datasheet june 2008" only documents those three options.
They are set using 3 bits. The documententation also makes mention
of 4mb, 16mb, 32mb, 48mb, 64mb but not how to set it.

The other non documented (straight forward) bit combinations allow
to change the VRAM size to those other states.

What this patch does is:
- add those undocumented registers with their respective vram size to
the i945 NB code;
- make this a cmos option on targets that have this northbridge.

TEST: build, flash to target, set cmos as desired and boot linux.
On Debian it can be found using "dmesg | grep stolen".
NOTE: dmesg message about reserved vram are quite different depending
on linux version

Change-Id: Ia71367ae3efb51bd64affd728407b8386e74594f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/14819
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

5 files changed, 26 insertions, 27 deletions

diff --git a/src/northbridge/intel/i945/early_init.c b/src/northbridge/intel/i945/early_init.c
index ade120f442..f4d091696e 100644
--- a/src/northbridge/intel/i945/early_init.c
+++ b/src/northbridge/intel/i945/early_init.c
@@ -23,6 +23,7 @@
 #include <halt.h>
 #include <string.h>
 #include "i945.h"
+#include <pc80/mc146818rtc.h>
 
 int i945_silicon_revision(void)
 {
@@ -145,7 +146,7 @@ static void i945_detect_chipset(void)
 
 static void i945_setup_bars(void)
 {
-	u8 reg8;
+	u8 reg8, gfxsize;
 
 	/* As of now, we don't have all the A0 workarounds implemented */
 	if (i945_silicon_revision() == 0)
@@ -178,10 +179,13 @@ static void i945_setup_bars(void)
 	pci_write_config32(PCI_DEV(0, 0x00, 0), DMIBAR, (uintptr_t)DEFAULT_DMIBAR | 1);
 	pci_write_config32(PCI_DEV(0, 0x00, 0), X60BAR, DEFAULT_X60BAR | 1);
 
-	/* Hardware default is 8MB UMA. If someone wants to make this a
-	 * CMOS or compile time option, send a patch.
-	 * pci_write_config16(PCI_DEV(0, 0x00, 0), GGC, 0x30);
-	 */
+	/* vram size from cmos option */
+	if (get_option(&gfxsize, "gfx_uma_size") != CB_SUCCESS)
+		gfxsize = 2;	/* 2 for 8MB */
+	/* make sure no invalid setting is used */
+	if (gfxsize > 6)
+		gfxsize = 2;
+	pci_write_config16(PCI_DEV(0, 0x00, 0), GGC, ((gfxsize + 1) << 4));
 
 	/* Set C0000-FFFFF to access RAM on both reads and writes */
 	pci_write_config8(PCI_DEV(0, 0x00, 0), PAM0, 0x30);
diff --git a/src/northbridge/intel/i945/gma.c b/src/northbridge/intel/i945/gma.c
index df13ef4950..02caa0a37a 100644
--- a/src/northbridge/intel/i945/gma.c
+++ b/src/northbridge/intel/i945/gma.c
@@ -353,17 +353,7 @@ static int intel_gma_init(struct northbridge_intel_i945_config *conf,
 	reg16 = pci_read_config16(dev_find_slot(0, PCI_DEVFN(0, 0)), GGC);
 	uma_size = 0;
 	if (!(reg16 & 2)) {
-		reg16 >>= 4;
-		reg16 &= 7;
-		switch (reg16) {
-		case 1:
-			uma_size = 1024;
-			break;
-		case 3:
-			uma_size = 8192;
-			break;
-		}
-
+		uma_size = decode_igd_memory_size((reg16 >> 4) & 7);
 		printk(BIOS_DEBUG, "%dM UMA\n", uma_size >> 10);
 	}
 
diff --git a/src/northbridge/intel/i945/i945.h b/src/northbridge/intel/i945/i945.h
index 0536a36d71..a7a3c5ccd3 100644
--- a/src/northbridge/intel/i945/i945.h
+++ b/src/northbridge/intel/i945/i945.h
@@ -364,6 +364,8 @@ void dump_pci_devices(void);
 void dump_spd_registers(void);
 void dump_mem(unsigned start, unsigned end);
 
+u32 decode_igd_memory_size(u32 gms);
+
 #endif /* __ACPI__ */
 
 #endif /* NORTHBRIDGE_INTEL_I945_H */
diff --git a/src/northbridge/intel/i945/northbridge.c b/src/northbridge/intel/i945/northbridge.c
index 514f88c8af..719a7954f2 100644
--- a/src/northbridge/intel/i945/northbridge.c
+++ b/src/northbridge/intel/i945/northbridge.c
@@ -104,18 +104,8 @@ static void pci_domain_set_resources(device_t dev)
 	/* Note: subtract IGD device and TSEG */
 	reg16 = pci_read_config16(dev_find_slot(0, PCI_DEVFN(0, 0)), GGC);
 	if (!(reg16 & 2)) {
-		int uma_size = 0;
 		printk(BIOS_DEBUG, "IGD decoded, subtracting ");
-		reg16 >>= 4;
-		reg16 &= 7;
-		switch (reg16) {
-		case 1:
-			uma_size = 1024;
-			break;
-		case 3:
-			uma_size = 8192;
-			break;
-		}
+		int uma_size = decode_igd_memory_size((reg16 >> 4) & 7);
 
 		printk(BIOS_DEBUG, "%dM UMA\n", uma_size >> 10);
 		tomk_stolen -= uma_size;
diff --git a/src/northbridge/intel/i945/ram_calc.c b/src/northbridge/intel/i945/ram_calc.c
index b161431e15..4349d19ea7 100644
--- a/src/northbridge/intel/i945/ram_calc.c
+++ b/src/northbridge/intel/i945/ram_calc.c
@@ -19,6 +19,7 @@
 #include <arch/io.h>
 #include <cbmem.h>
 #include "i945.h"
+#include <console/console.h>
 
 static uintptr_t smm_region_start(void)
 {
@@ -56,3 +57,15 @@ void *cbmem_top(void)
 {
 	return (void *) smm_region_start();
 }
+
+/** Decodes used Graphics Mode Select (GMS) to kilobytes. */
+u32 decode_igd_memory_size(const u32 gms)
+{
+	static const u16 ggc2uma[] = { 0, 1, 4, 8, 16, 32,
+			48, 64 };
+
+	if (gms > ARRAY_SIZE(ggc2uma))
+		die("Bad Graphics Mode Select (GMS) setting.\n");
+
+	return ggc2uma[gms] << 10;
+}