From bbee219bab918e5a1d43031a27475dcdffea5dc5 Mon Sep 17 00:00:00 2001
From: turbocat <turbocat@kolibrios.org>
Date: Tue, 26 Dec 2023 18:33:21 +0000
Subject: [PATCH] [KERNEL] Use PAT if supported. Otherwise MTRR

git-svn-id: svn://kolibrios.org@9950 a494cfbc-eb01-0410-851d-a64ba20cac60
---
 kernel/trunk/core/mtrr.inc     | 28 ++++++++++++++--------------
 kernel/trunk/core/mtrrtest.asm |  6 +++---
 kernel/trunk/kernel.asm        |  2 +-
 3 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/kernel/trunk/core/mtrr.inc b/kernel/trunk/core/mtrr.inc
index 6eef4ae5ae..36f23b2409 100644
--- a/kernel/trunk/core/mtrr.inc
+++ b/kernel/trunk/core/mtrr.inc
@@ -7,12 +7,22 @@
 
 $Revision$
 
-; Initializes MTRRs.
-proc init_mtrr
-
+; Initializes PAT (Page Attribute Table) and MTRRs.
+proc init_pat_mtrr
         cmp     [BOOT.mtrr], byte 2
         je      .exit
 
+        bt      [cpu_caps], CAPS_PAT    ; if PAT is not supported, use MTRR
+        jnc     .use_mtrr
+
+; Change PAT_MSR for write combining memory.
+        mov     ecx, MSR_CR_PAT
+        mov     eax, PAT_VALUE          ; UC UCM WC WB
+        mov     edx, eax
+        wrmsr
+        ret
+
+.use_mtrr:
         bt      [cpu_caps], CAPS_MTRR
         jnc     .exit
 
@@ -739,17 +749,7 @@ end virtual
         jmp     @b
 @@:
 
-; 9i. Check PAT support and reprogram PAT_MASR for write combining memory
-        bt      [cpu_caps], CAPS_PAT
-        jnc     @F
-
-        mov     ecx, MSR_CR_PAT
-        mov     eax, PAT_VALUE  ;UC UCM WC WB
-        mov     edx, eax
-        wrmsr
-@@:
-
-; 9j. Changes are done.
+; 9i. Changes are done.
         call    mtrr_end_change
 
 .abort:
diff --git a/kernel/trunk/core/mtrrtest.asm b/kernel/trunk/core/mtrrtest.asm
index dede91186a..d8694e3ae8 100644
--- a/kernel/trunk/core/mtrrtest.asm
+++ b/kernel/trunk/core/mtrrtest.asm
@@ -18,12 +18,12 @@ entry start
 MAX_VARIABLE_MTRR = 10
 
 start:
-; Copy test inputs, run init_mtrr, compare with test outputs. Repeat.
+; Copy test inputs, run init_pat_mtrr, compare with test outputs. Repeat.
         mov     esi, test1_in_data
         mov     edi, mtrrdata
         mov     ecx, mtrrdata_size / 4
         rep movsd
-        call    init_mtrr
+        call    init_pat_mtrr
         mov     esi, test1_out_data
         mov     edi, mtrrdata
         mov     ecx, mtrrdata_size / 4
@@ -33,7 +33,7 @@ start:
         mov     edi, mtrrdata
         mov     ecx, mtrrdata_size / 4
         rep movsd
-        call    init_mtrr
+        call    init_pat_mtrr
         mov     esi, test2_out_data
         mov     edi, mtrrdata
         mov     ecx, mtrrdata_size / 4
diff --git a/kernel/trunk/kernel.asm b/kernel/trunk/kernel.asm
index 5ab1ec71e5..a6139d450f 100644
--- a/kernel/trunk/kernel.asm
+++ b/kernel/trunk/kernel.asm
@@ -436,7 +436,7 @@ high_code:
         list_init eax
 
         call    init_video
-        call    init_mtrr
+        call    init_pat_mtrr
         mov     [LFBAddress], LFB_BASE
         mov     ecx, bios_fb
         call    set_framebuffer