source: mainline/boot/arch/arm32/src/mm.c@ 4b27f5f

/*
 * Copyright (c) 2007 Pavel Jancik, Michal Kebrt
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup arm32boot
 * @{
 */
/** @file
 * @brief Memory management used while booting the kernel.
 */

#include <typedefs.h>
#include <arch/asm.h>
#include <arch/mm.h>

/** Disable the MMU */
static void disable_paging(void)
{
        asm volatile (
                "mrc p15, 0, r0, c1, c0, 0\n"
                "bic r0, r0, #1\n"
                "mcr p15, 0, r0, c1, c0, 0\n"
                ::: "r0"
        );
}

/** Check if caching can be enabled for a given memory section.
 *
 * Memory areas used for I/O are excluded from caching.
 * At the moment caching is enabled only on GTA02.
 *
 * @param section       The section number.
 *
 * @return      1 if the given section can be mapped as cacheable, 0 otherwise.
*/
static inline int section_cacheable(pfn_t section)
{
#ifdef MACHINE_gta02
        unsigned long address = section << PTE_SECTION_SHIFT;

        if (address >= GTA02_IOMEM_START && address < GTA02_IOMEM_END)
                return 0;
        else
                return 1;
#elif defined MACHINE_beagleboardxm
        const unsigned long address = section << PTE_SECTION_SHIFT;
        if (address >= BBXM_RAM_START && address < BBXM_RAM_END)
                return 1;
#elif defined MACHINE_beaglebone
        const unsigned long address = section << PTE_SECTION_SHIFT;
        if (address >= AM335x_RAM_START && address < AM335x_RAM_END)
                return 1;
#endif
        return 0;
}

/** Initialize "section" page table entry.
 *
 * Will be readable/writable by kernel with no access from user mode.
 * Will belong to domain 0. No cache or buffering is enabled.
 *
 * @param pte   Section entry to initialize.
 * @param frame First frame in the section (frame number).
 *
 * @note If frame is not 1 MB aligned, first lower 1 MB aligned frame will be
 *       used.
 *
 */
static void init_ptl0_section(pte_level0_section_t* pte,
    pfn_t frame)
{
        pte->descriptor_type = PTE_DESCRIPTOR_SECTION;
        pte->bufferable = 1;
        pte->cacheable = section_cacheable(frame);
        pte->xn = 0;
        pte->domain = 0;
        pte->should_be_zero_1 = 0;
        pte->access_permission_0 = PTE_AP_USER_NO_KERNEL_RW;
        pte->tex = 0;
        pte->access_permission_1 = 0;
        pte->shareable = 0;
        pte->non_global = 0;
        pte->should_be_zero_2 = 0;
        pte->non_secure = 0;
        pte->section_base_addr = frame;
}

/** Initialize page table used while booting the kernel. */
static void init_boot_pt(void)
{
        const pfn_t split_page = PTL0_ENTRIES;
        /* Create 1:1 virtual-physical mapping (in lower 2 GB). */
        pfn_t page;
        for (page = 0; page < split_page; page++)
                init_ptl0_section(&boot_pt[page], page);
        
        asm volatile (
                "mcr p15, 0, %[pt], c2, c0, 0\n"
                :: [pt] "r" (boot_pt)
        );
}

static void enable_paging()
{
        /* c3   - each two bits controls access to the one of domains (16)
         * 0b01 - behave as a client (user) of a domain
         */
        asm volatile (
                /* Behave as a client of domains */
                "ldr r0, =0x55555555\n"
                "mcr p15, 0, r0, c3, c0, 0\n"

                /* Current settings */
                "mrc p15, 0, r0, c1, c0, 0\n"
                
                /* Enable ICache, DCache, BPredictors and MMU,
                 * we disable caches before jumping to kernel
                 * so this is safe for all archs.
                 * Enable VMSAv6 the bit (23) is only writable on ARMv6.
                 */
                "ldr r1, =0x00801805\n"
                
                "orr r0, r0, r1\n"

                /* Invalidate the TLB content before turning on the MMU.
                 * ARMv7-A Reference manual, B3.10.3
                 */
                "mcr p15, 0, r0, c8, c7, 0\n"
                
                /* Store settings, enable the MMU */
                "mcr p15, 0, r0, c1, c0, 0\n"
                ::: "r0", "r1"
        );
}

/** Start the MMU - initialize page table and enable paging. */
void mmu_start() {
        disable_paging();
        init_boot_pt();
        enable_paging();
}

/** @}
 */