[PATCH v2 2/6] x86: fsp: Use mtrr_set_next_var() for graphics memory

Bin Meng bmeng at tinylab.org
Mon Jul 31 08:01:04 CEST 2023

From: Bin Meng <bmeng.cn at gmail.com>

At present this uses mtrr_add_request() & mtrr_commit() combination
to program the MTRR for graphics memory. This usage has two major
issues as below:

- mtrr_commit() will re-initialize all MTRR registers from index 0,
  using the settings previously added by mtrr_add_request() and saved
  in gd->arch.mtrr_req[], which won't cause any issue but is unnecessary
- The way such combination works is based on the assumption that U-Boot
  has full control with MTRR programming (e.g.: U-Boot without any blob
  that does all low-level initialization on its own, or using FSP2 which
  does not touch MTRR), but this is not the case with FSP. FSP programs
  some MTRRs during its execution but U-Boot does not have the settings
  saved in gd->arch.mtrr_req[] and when doing mtrr_commit() it will
  corrupt what was already programmed previously.

Correct this to use mtrr_set_next_var() instead.

Signed-off-by: Bin Meng <bmeng.cn at gmail.com>

(no changes since v1)

 arch/x86/lib/fsp/fsp_graphics.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/lib/fsp/fsp_graphics.c b/arch/x86/lib/fsp/fsp_graphics.c
index 2bcc49f605..09d5da8c84 100644
--- a/arch/x86/lib/fsp/fsp_graphics.c
+++ b/arch/x86/lib/fsp/fsp_graphics.c
@@ -110,8 +110,7 @@ static int fsp_video_probe(struct udevice *dev)
 	if (ret)
 		goto err;
-	mtrr_add_request(MTRR_TYPE_WRCOMB, vesa->phys_base_ptr, 256 << 20);
-	mtrr_commit(true);
+	mtrr_set_next_var(MTRR_TYPE_WRCOMB, vesa->phys_base_ptr, 256 << 20);
 	printf("%dx%dx%d @ %x\n", uc_priv->xsize, uc_priv->ysize,
 	       vesa->bits_per_pixel, vesa->phys_base_ptr);

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