Changes in boot/arch/arm32/src/mm.c [accdbd8:c5429fe] in mainline

File:

• boot/arch/arm32/src/mm.c (modified) (2 diffs)

boot/arch/arm32/src/mm.c

@@ -99 +99 @@
  *
  * Memory areas used for I/O are excluded from caching.
+ * At the moment caching is enabled only on GTA02.
  *
  * @param section       The section number.
@@ -170 +171 @@
 {
         /*
-         * Our goal is to create page tables that serve two purposes:
-         *
-         * 1. Allow the loader to run in identity-mapped virtual memory and use
-         *    I/O devices (e.g. an UART for logging).
-         * 2. Allow the kernel to start running in virtual memory from addresses
-         *    above 2G.
-         *
-         * The matters are slightly complicated by the different locations of
-         * physical memory and I/O devices on the various boards that we
-         * support. We see two cases (but other are still possible):
-         *
-         * a) Both RAM and I/O is in memory below 2G
-         *    For instance, this is the case of GTA02, Integrator/CP
-         *    and RaspberryPi
-         * b) RAM starts at 2G and I/O devices are below 2G
-         *    For example, this is the case of BeagleBone and BeagleBoard XM
-         *
-         * This leads to two possible setups of boot page tables:
-         *
-         * A) To arrange for a), split the virtual address space into two
-         *    halves, both identity-mapping the first 2G of physical address
-         *    space.
-         * B) To accommodate b), create one larger virtual address space
-         *    identity-mapping the entire physical address space.
-         */
-
-        for (pfn_t page = 0; page < PTL0_ENTRIES; page++) {
-                pfn_t frame = page;
-                if (BOOT_BASE < 0x80000000UL && page >= PTL0_ENTRIES / 2)
-                        frame -= PTL0_ENTRIES / 2;
-                init_ptl0_section(&boot_pt[page], frame);
-        }
+         * Create 1:1 virtual-physical mapping.
+         * Physical memory on BBxM a BBone starts at 2GB
+         * boundary, icp has a memory mirror at 2GB.
+         * (ARM Integrator Core Module User guide ch. 6.3,  p. 6-7)
+         * gta02 somehow works (probably due to limited address size),
+         * s3c2442b manual ch. 5, p.5-1:
+         * "Address space: 128Mbytes per bank (total 1GB/8 banks)"
+         */
+        for (pfn_t page = 0; page < PTL0_ENTRIES; ++page)
+                init_ptl0_section(&boot_pt[page], page);
 
         /*