From 39145f6d1b8c57abe2bc0167b2b413970d0dfdb6 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Tue, 19 Nov 2019 17:49:20 +0100
Subject: split kernel into more files

---
 paging.c | 114 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 paging.c

(limited to 'paging.c')

diff --git a/paging.c b/paging.c
new file mode 100644
index 0000000..7c2a9de
--- /dev/null
+++ b/paging.c
@@ -0,0 +1,114 @@
+#include "cp_regs.h"
+#include "uart.h"
+#include "strings.h"
+#include "memory.h"
+#include "translation_table_descriptors.h"
+
+void setup_flat_map(void)
+{
+  char bits[33]; // for printing uint32_t bit values
+  
+  // compute translation table base address
+  // translation table shall start at first 2^14-bytes aligned
+  // address after the kernel image
+
+  uint32_to_bits(TRANSLATION_TABLE_BASE, bits);
+  uart_puts("binary representation of chosen"
+	    " lvl1 translation table address: ");
+  uart_puts(bits); uart_puts("\n\r");
+ 
+  // flat map all memory
+  uart_puts("preparing translation table\n\r");
+  short_descriptor_lvl1_t volatile *translation_table =
+    (short_descriptor_lvl1_t*) TRANSLATION_TABLE_BASE;
+  
+  for (uint32_t i = 0; i < 4096; i++)
+      translation_table[i].section_fields =
+	(short_section_descriptor_t) {
+	.SECTION_BASE_ADDRESS_31_20  = i,
+	.SECTION_OR_SUPERSECTION_BIT = DESCRIBES_SECTION,
+	.ACCESS_PERMISSIONS_2        = AP_2_0_MODEL_RW_PL1 >> 2,
+	.ACCESS_PERMISSIONS_1_0      = AP_2_0_MODEL_RW_PL1 & 0b011,
+	.DESCRIPTOR_TYPE_1           =
+	   SHORT_DESCRIPTOR_SECTION_OR_SUPERSECTION >> 1,
+	// rest of fields are 0s
+      };
+
+  // meddle with domain settings
+  uart_puts("setting domain0 to client access"
+	    " and blocking other domains\n\r");
+
+  DACR_t DACR = 0;
+  DACR = set_domain_permissions(DACR, 0, DOMAIN_CLIENT_ACCESS);
+  for (int i = 1; i < 16; i++)
+    DACR = set_domain_permissions(DACR, i, DOMAIN_NO_ACCESS);
+
+  // the above should do the same as this:
+  // DACR = 1;
+  
+  asm("mcr p15, 0, %0, c3, c0, 0" :: "r" (DACR));
+
+  // meddle with SCTLR, which determines how some bits in
+  // table descriptors work and also controls caches
+  // we don't want to use access flag, so we set AFE to 0
+  // we don't want TEX remap, so we set TRE to 0
+  // we also disable data and instruction caches and the MMU
+  
+  // some of this is redundant (i.e. MMU should already be disabled)
+  uart_puts("setting C, I, AFE and TRE to 0 in SCTLR\n\r");
+
+  SCTLR_t SCTLR;
+  asm("mrc p15, 0, %0, c1, c0, 0" : "=r" (SCTLR.raw));
+
+  SCTLR.fields.M   = 0; // disable MMU
+  SCTLR.fields.C   = 0; // disable data cache
+  SCTLR.fields.I   = 0; // disable instruction cache
+  SCTLR.fields.TRE = 0; // disable TEX remap
+  SCTLR.fields.AFE = 0; // disable access flag usage
+  asm("mcr p15, 0, %0, c1, c0, 0\n\r"
+      "isb" :: "r" (SCTLR.raw) : "memory");
+
+  // TODO: move invalidation instructions to some header as inlines
+  
+  uart_puts("invalidating instruction cache, branch prediction,"
+	    " and entire main TLB\n\r");
+  
+  // invalidate instruction cache
+  asm("mcr p15, 0, r0, c7, c5, 0\n\r" // r0 gets ignored
+      "isb" ::: "memory");
+
+  // invalidate branch-prediction
+  asm("mcr p15, 0, r0, c7, c5, 6\n\r" // r0 - same as above
+      "isb" ::: "memory");
+
+  // invalidate main Translation Lookup Buffer
+  asm("mcr p15, 0, %0, c8, c7, 0\n\r"
+      "isb" :: "r" (0) : "memory");
+
+  // now set TTBCR to use TTBR0 exclusively
+  uart_puts("Setting TTBCR.N to 0, so that"
+	    " TTBR0 is used everywhere\n\r");
+  
+  uint32_t TTBCR = 0;
+  asm("mcr p15, 0, %0, c2, c0, 2" :: "r" (TTBCR));
+  
+  // Now do stuff with TTBR0
+  TTBR_t TTBR0;
+  TTBR0.raw = 0;
+  TTBR0.fields.TTBR_TRANSLATION_TABLE_BASE_ADDRESS =
+    TRANSLATION_TABLE_BASE >> 14;
+  // rest of TTBR0 remains 0s
+  
+  asm("mcr p15, 0, %0, c2, c0, 0" :: "r" (TTBR0.raw));
+
+  // enable MMU
+  uart_puts("enabling the MMU\n\r");
+
+  // redundant - we already have SCTLR contents in the variable
+  // asm("mrc p15, 0, %0, c1, c0, 0" : "=r" (SCTLR.raw));
+
+  SCTLR.fields.M = 1;
+
+  asm("mcr p15, 0, %0, c1, c0, 0\n\r"
+      "isb" :: "r" (SCTLR.raw) : "memory");
+}
-- 
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