svn commit: r292523 - head/sys/arm/arm

Sun Dec 20 23:31:13 UTC 2015

Author: ian
Date: Sun Dec 20 23:31:11 2015
New Revision: 292523
URL: https://svnweb.freebsd.org/changeset/base/292523

Log:
  Allow armv4/5 kernels to be loaded on any 2MB boundary, like armv6/7.
  
  This eliminates the reliance on PHYSADDR and KERNPHYSADDR compile-time
  symbols (except when the rom-copy code is enabled) by using the current
  PC and the assumption that the entry-point routine is in the first 1MB
  section of the text segment.
  
  Other cleanups done:
  
   - Reduce the initarm() stack size back to 2K.  It got increased to
     4 * 2K when this file was supporting multicore armv6, but that
     support is now in locore-v6.S.
  
   - When building the temporary startup page tables, map the entire
     4GB address space as VA=PA before mapping the kernel at its loaded
     location.  This allows access to boot parameters stored somewhere
     in ram by the bootloader, regardless of where that may be.
  
   - When building the page table entry for supporting EARLY_PRINTF, map
     the section as uncached unbuffered, since it is presumably device
     registers.
  
  Note that this restores the ability to use loader(8)/ubldr on armv4/5
  kernels.  That was broken in r283035, the point at which ubldr started
  loading an arm kernel at any 2MB boundary.
  
  Also note that after this, there is no reason to set KERNVIRTADDR to
  anything other than 0xc0000000, and no need for PHYSADDR or KERNPHYSADDR
  symbols at all.

Modified:
  head/sys/arm/arm/locore-v4.S

Modified: head/sys/arm/arm/locore-v4.S
==============================================================================

--- head/sys/arm/arm/locore-v4.S	Sun Dec 20 23:22:04 2015	(r292522)
+++ head/sys/arm/arm/locore-v4.S	Sun Dec 20 23:31:11 2015	(r292523)
@@ -42,19 +42,8 @@
 
 __FBSDID("$FreeBSD$");
 
-/*
- * Sanity check the configuration.
- * FLASHADDR and LOADERRAMADDR depend on PHYSADDR in some cases.
- * ARMv4 and ARMv5 make assumptions on where they are loaded.
- *
- * TODO: Fix the ARMv4/v5 case.
- */
-#ifndef PHYSADDR
-#error PHYSADDR must be defined for this configuration
-#endif
-
-/* What size should this really be ? It is only used by initarm() */
-#define INIT_ARM_STACK_SIZE	(2048 * 4)
+/* 2K initial stack is plenty, it is only used by initarm() */
+#define INIT_ARM_STACK_SIZE	2048
 
 #define	CPWAIT_BRANCH							 \
 	sub	pc, pc, #4
@@ -109,6 +98,16 @@ ASENTRY_NP(_start)
 	msr	cpsr_c, r7
 
 #if defined (FLASHADDR) && defined(LOADERRAMADDR)
+/*
+ * Sanity check the configuration.
+ * FLASHADDR and LOADERRAMADDR depend on PHYSADDR in some cases.
+ * ARMv4 and ARMv5 make assumptions on where they are loaded.
+ * TODO: Fix the ARMv4/v5 case.
+ */
+#ifndef PHYSADDR
+#error PHYSADDR must be defined for this configuration
+#endif
+
 	/* Check if we're running from flash. */
 	ldr	r7, =FLASHADDR
 	/*
@@ -164,37 +163,45 @@ Lunmapped:
 	 * Build page table from scratch.
 	 */
 
-	/* Find the delta between VA and PA */
+	/* 
+	 * Figure out the physical address we're loaded at by assuming this
+	 * entry point code is in the first L1 section and so if we clear the
+	 * offset bits of the pc that will give us the section-aligned load
+	 * address, which remains in r5 throughout all the following code.
+	 */
+	ldr	r2, =(L1_S_OFFSET)
+	bic	r5, pc, r2
+
+	/* Find the delta between VA and PA, result stays in r0 throughout. */
 	adr	r0, Lpagetable
 	bl	translate_va_to_pa
 
-	/*
-	 * Some of the older ports (the various XScale, mostly) assume
-	 * that the memory before the kernel is mapped, and use it for
-	 * the various stacks, page tables, etc. For those CPUs, map the
-	 * 64 first MB of RAM, as it used to be.
-	 */
-	/*
-	 * Map PA == VA
+	/* 
+	 * First map the entire 4GB address space as VA=PA.  It's mapped as
+	 * normal (cached) memory because it's for things like accessing the
+	 * parameters passed in from the bootloader, which might be at any
+	 * physical address, different for every platform.
 	 */
-	ldr	r5, =PHYSADDR
-	mov	r1, r5
-	mov	r2, r5
-	/* Map 64MiB, preserved over calls to build_pagetables */
-	mov	r3, #64
+	mov	r1, #0
+	mov	r2, #0
+	mov	r3, #4096
 	bl	build_pagetables
 
-	/* Create the kernel map to jump to */
+	/* 
+	 * Next we do 64MiB starting at the physical load address, mapped to
+	 * the VA the kernel is linked for.
+	 */
 	mov	r1, r5
-	ldr	r2, =(KERNBASE)
+	ldr	r2, =(KERNVIRTADDR)
+	mov	r3, #64
 	bl	build_pagetables
-	ldr	r5, =(KERNPHYSADDR)
 
+	/* Create a device mapping for early_printf if specified. */
 #if defined(SOCDEV_PA) && defined(SOCDEV_VA)
-	/* Create the custom map */
 	ldr	r1, =SOCDEV_PA
 	ldr	r2, =SOCDEV_VA
-	bl	build_pagetables
+	mov	r3, #1
+	bl	build_device_pagetables
 #endif
 
 	mcr	p15, 0, r0, c2, c0, 0	/* Set TTB */
@@ -205,9 +212,6 @@ Lunmapped:
 	mcr	p15, 0, r0, c3, c0, 0
 	/*
 	 * Enable MMU.
-	 * On armv6 enable extended page tables, and set alignment checking
-	 * to modulo-4 (CPU_CONTROL_UNAL_ENABLE) for the ldrd/strd
-	 * instructions emitted by clang.
 	 */
 	mrc	p15, 0, r0, c1, c0, 0
 	orr	r0, r0, #(CPU_CONTROL_MMU_ENABLE)
@@ -217,6 +221,9 @@ Lunmapped:
 	nop
 	CPWAIT(r0)
 
+	/* Transition the PC from physical to virtual addressing. */
+	ldr	pc,=mmu_done
+
 mmu_done:
 	nop
 	adr	r1, .Lstart
@@ -227,7 +234,6 @@ mmu_done:
 	str	r3, [r1], #0x0004	/* get zero init data */
 	subs	r2, r2, #4
 	bgt	.L1
-	ldr	pc, .Lvirt_done
 
 virt_done:
 	mov	r1, #28			/* loader info size is 28 bytes also second arg */
@@ -301,21 +307,25 @@ translate_va_to_pa:
  *
  * Addresses must be 1MiB aligned
  */
+build_device_pagetables:
+	ldr	r4, =(L1_TYPE_S|L1_S_AP(AP_KRW))
+	b	1f
 build_pagetables:
 	/* Set the required page attributed */
 	ldr	r4, =(L1_TYPE_S|L1_S_C|L1_S_AP(AP_KRW))
+1:
 	orr	r1, r4
 
 	/* Move the virtual address to the correct bit location */
 	lsr	r2, #(L1_S_SHIFT - 2)
 
 	mov	r4, r3
-1:
+2:
 	str	r1, [r0, r2]
 	add	r2, r2, #4
 	add	r1, r1, #(L1_S_SIZE)
 	adds	r4, r4, #-1
-	bhi	1b
+	bhi	2b
 
 	RET
 
