Patch set updated for coreboot: 581ca4f intel/i945/gma: Place GTT below top of memory

[Francis Rowe]

Francis Rowe ([e-mail]) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/5927

-gerrit

commit 581ca4ff46831f5c5e5c4e876b3fd1db43fd601e
Author: Paul Menzel 
Date:   Thu Jun 5 22:45:35 2014 +0200

intel/i945/gma: Place GTT below top of memory

Since commit 17fec8a0 [1]

drm/i915: Use Graphics Base of Stolen Memory on all gen3+

present in the Linux kernel since version 3.12, 3D does not work
    anymore [2].

Comparing the graphics registers, in this case that means output of
    `intel_reg_dumper`, the vendor Video BIOS is setting the register
    PGTBL_CTL/PGETBL_CTL, only documented in the i965 datasheet [3], to
    `0x3ffc0001` on a system with 1 GB of RAM, while native graphics init
    sets it to `0x3f800001`.

Currently native graphis init sets the GTT right above the base
    address of stolen memory. The Video BIOS sets it below the top of
    memory.  The Linux Intel driver expects it to be below top of memory, so
    do it this way, by setting the address to TOM minus the size of the GTT,
    which is hardcoded to 256 KiB.

As `PGETBL_CTL` is zero by default, reading its value in the beginning
    is not necessary and is only confusing. Make it clear that the code
    calculates the value.

There is still a PTE error reported during boot, but 3D works
    with Linux 3.12+ and no user visible problems are shown.

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=1...
    [2] https://bugs.freedesktop.org/show_bug.cgi?id=79038
    [3] https://01.org/linuxgraphics/sites/default/files/documentation/965_g35_vol_1...
        Intel ® 965 Express Chipset Family and
          Intel ® G35 Express Chipset Graphics Controller
          Programmer’s Reference Manual
        Volume 1: Graphics Core
        Revision 1.0a

Change-Id: I0a5b04c2c5300f5056cb48075aa5804984bc9948
    Signed-off-by: Paul Menzel 
    Signed-off-by: Francis Rowe 
---
 src/northbridge/intel/i945/gma.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/northbridge/intel/i945/gma.c b/src/northbridge/intel/i945/gma.c
index 140aaa7..e8a57b1 100644
--- a/src/northbridge/intel/i945/gma.c
+++ b/src/northbridge/intel/i945/gma.c
@@ -52,11 +52,19 @@
 static int gtt_setup(unsigned int mmiobase)
 {
    unsigned long PGETBL_save;
-
-	PGETBL_save = read32(mmiobase + PGETBL_CTL) & ~PGETBL_ENABLED;
+	unsigned long tom; // top of memory
+
+	/*
+	 * The Video BIOS places the GTT right below top of memory.
+	 *
+	 * It is not documented in the Intel 945 datasheet, but the Intel
+	 * developers said that it is normally placed there.
+	 *
+	 * TODO: Add option to make the GTT size runtime configurable
+	*/
+	tom = pci_read_config8(dev_find_slot(0, PCI_DEVFN(0, 0)), TOLUD) << 24;
+	PGETBL_save = tom - 256 * KiB;
    PGETBL_save |= PGETBL_ENABLED;
-
-	PGETBL_save |= pci_read_config32(dev_find_slot(0, PCI_DEVFN(2,0)), 0x5c) & 0xfffff000;
    PGETBL_save |= 2; /* set GTT to 256kb */

write32(mmiobase + GFX_FLSH_CNTL, 0);