/*
 * @author  xamidev <xamidev@riseup.net>
 * @brief   x86 architecture-dependant initialization
 * @license GPL-3.0-only
 */

#include <mem/gdt.h>
#include <stdint.h>
#include <arch/x86.h>
#include <kernel.h>

/*
 * x86_overwrite_pat - Set PAT to WC
 *
 * This function overwrites the 1st Page Attribute
 * Table entry, to enable the Write-Combining property
 * when we map memory regions later on.
 * The framebuffer will be mapped with WC, which makes
 * memory access significantly faster by using burst
 * operations. 
*/

static void x86_overwrite_pat()
{
    uint64_t pat = rdmsr(0x277);
    pat &= ~(0xFFULL << 8); // Clear PAT1
    pat |= (0x01ULL << 8); // PAT1 = 0x01 (WC)
    wrmsr(0x277, pat);
}

/*
 * x86_arch_init - Initialize x86 CPU structures
 *
 * This function is responsible for overriding a PAT entry
 * (to put the framebuffer area in WC mode) only.
 *
 * Later, all architecture-dependant init (GDT, IDT, TSS, ...)
 * should be initialized here, and separate function pointers
 * should be set up for each arch.
 */
void x86_arch_init()
{
    x86_overwrite_pat();
    idt_init();
    gdt_init();
}