PATCH 1/4][v4] doc:Add documentation for e500 external debugger support

This describes requirement of e500 and e500v2 processor to support external
debugger.

It also provide an insight of the configuration switch required and their
description.

Signed-off-by: Radu Lazarescu <radu.lazarescu@freescale.com>
Signed-off-by: Marius Grigoras <marius.grigoras@freescale.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>

1 files changed, 166 insertions, 0 deletions

diff --git a/doc/README.mpc85xx b/doc/README.mpc85xx
new file mode 100644
index 0000000000..2753b45b0b
--- /dev/null
+++ b/doc/README.mpc85xx
@@ -0,0 +1,166 @@
+External Debug Support
+----------------------
+
+Freescale's e500v1 and e500v2 cores (used in mpc85xx chips) have some
+restrictions on external debugging (JTAG).  In particular, for the debugger to
+be able to receive control after a single step or breakpoint:
+	- MSR[DE] must be set
+	- A valid opcode must be fetchable, through the MMU, from the debug
+	  exception vector (IVPR + IVOR15).
+
+To maximize the time during which this requirement is met, U-Boot sets MSR[DE]
+immediately on entry and keeps it set. It also uses a temporary TLB to keep a
+mapping to a valid opcode at the debug exception vector, even if we normally
+don't support exception vectors being used that early, and that's not the area
+where U-Boot currently executes from.
+
+Note that there may still be some small windows where debugging will not work,
+such as in between updating IVPR and IVOR15.
+
+Config Switches:
+----------------
+
+Please refer README section "MPC85xx External Debug Support"
+
+Major Config Switches during various boot Modes
+----------------------------------------------
+
+NOR boot
+                !defined(CONFIG_SYS_RAMBOOT)
+NOR boot Secure
+                !defined(CONFIG_SYS_RAMBOOT) && defined(CONFIG_SECURE_BOOT)
+RAMBOOT(SD, SPI & NAND boot)
+                 defined(CONFIG_SYS_RAMBOOT)
+RAMBOOT Secure (SD, SPI & NAND)
+                 defined(CONFIG_SYS_RAMBOOT) && defined(CONFIG_SECURE_BOOT)
+NAND SPL BOOT
+                 defined(CONFIG_SYS_RAMBOOT) && defined(CONFIG_NAND_SPL)
+
+
+TLB Entries during u-boot execution
+-----------------------------------
+
+Note: Sequence number is in order of execution
+
+A) defined(CONFIG_SYS_RAMBOOT) i.e. SD, SPI, NAND RAMBOOT & NAND_SPL boot
+
+   1) TLB entry to overcome e500 v1/v2 debug restriction
+       Location   : Label "_start_e500"
+       TLB Entry  : CONFIG_SYS_PPC_E500_DEBUG_TLB
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE --> CONFIG_SYS_MONITOR_BASE
+       Properties : 256K, AS0, I, IPROT
+
+   2) TLB entry for working in AS1
+       Location   : Label "create_init_ram_area"
+       TLB Entry  : 15
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE --> CONFIG_SYS_MONITOR_BASE
+       Properties : 1M, AS1, I, G, IPROT
+
+   3) TLB entry for the stack during AS1
+       Location   : Lable "create_init_ram_area"
+       TLB Entry  : 14
+       EPN -->RPN : CONFIG_SYS_INIT_RAM_ADDR --> CONFIG_SYS_INIT_RAM_ADDR
+       Properties : 16K, AS1, IPROT
+
+   4) TLB entry for CCSRBAR during AS1 execution
+       Location   : cpu_init_early_f
+       TLB Entry  : 13
+       EPN -->RPN : CONFIG_SYS_CCSRBAR --> CONFIG_SYS_CCSRBAR
+       Properties : 1M, AS1, I, G
+
+   5) Invalidate unproctected TLB Entries
+       Location   : cpu_init_early_f
+       Invalidated: 13
+
+   6) Create TLB entries as per boards/freescale/<board>/tlb.c
+       Location   : cpu_init_early_f --> init_tlbs()
+       Properties : ..., AS0, ...
+      Please note It can overwrites previous TLB Entries.
+
+   7) Disable TLB Entries of AS1
+       Location   : cpu_init_f --> disable_tlb()
+       Disable    : 15, 14
+
+   8) Update Flash's TLB entry
+       Location   : Board_init_r
+       TLB entry  : Search from TLB entries
+       EPN -->RPN : CONFIG_SYS_FLASH_BASE --> CONFIG_SYS_FLASH_BASE_PHYS
+       Properties : Board specific size, AS0, I, G, IPROT
+
+
+B) !defined(CONFIG_SYS_RAMBOOT) i.e. NOR boot
+
+   1) TLB entry to overcome e500 v1/v2 debug restriction
+       Location   : Label "_start_e500"
+       TLB Entry  : CONFIG_SYS_PPC_E500_DEBUG_TLB
+#if defined(CONFIG_SECURE_BOOT)
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE --> CONFIG_SYS_PBI_FLASH_WINDOW
+       Properties : 1M, AS1, I, G, IPROT
+#else
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE & 0xffc00000 --> 0xffc00000
+       Properties : 4M, AS0, I, G, IPROT
+#endif
+
+   2) TLB entry for working in AS1
+       Location   : Label "create_init_ram_area"
+       TLB Entry  : 15
+#if defined(CONFIG_SECURE_BOOT)
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE --> CONFIG_SYS_PBI_FLASH_WINDOW
+       Properties : 1M, AS1, I, G, IPROT
+#else
+       EPN -->RPN : CONFIG_SYS_MONITOR_BASE & 0xffc00000 --> 0xffc00000
+       Properties : 4M, AS1, I, G, IPROT
+#endif
+
+   3) TLB entry for the stack during AS1
+       Location   : Lable "create_init_ram_area"
+       TLB Entry  : 14
+       EPN -->RPN : CONFIG_SYS_INIT_RAM_ADDR --> CONFIG_SYS_INIT_RAM_ADDR
+       Properties : 16K, AS1, IPROT
+
+   4) TLB entry for CCSRBAR during AS1 execution
+       Location   : cpu_init_early_f
+       TLB Entry  : 13
+       EPN -->RPN : CONFIG_SYS_CCSRBAR --> CONFIG_SYS_CCSRBAR
+       Properties : 1M, AS1, I, G
+
+   5) TLB entry for Errata workaround CONFIG_SYS_FSL_ERRATUM_IFC_A003399
+       Location   : cpu_init_early_f
+       TLB Entry  : 9
+       EPN -->RPN : SRAM_BASE_ADDR --> SRAM_BASE_ADDR
+       Properties : 1M, AS1, I
+
+   6) CONFIG_SYS_FSL_ERRATUM_IFC_A003399 Adjust flash's phys addr
+       Location   : cpu_init_early_f --> setup_ifc
+       TLB Entry  : Get Flash TLB
+       EPN -->RPN : Adjusted flash_phys --> Adjusted flash_phys
+       Properties : 4M, AS1, I, G, IPROT
+
+   7) CONFIG_SYS_FSL_ERRATUM_IFC_A003399: E500 v1,v2 debug restriction
+       Location   : cpu_init_early_f --> setup_ifc
+       TLB Entry  : CONFIG_SYS_PPC_E500_DEBUG_TLB
+       EPN -->RPN : Adjusted flash_phys --> Adjusted flash_phys
+       Properties : 4M, AS0, I, G, IPROT
+
+   8) Invalidate unproctected TLB Entries
+       Location   : cpu_init_early_f
+       Invalidated: 13, 9
+
+   9) Create TLB entries as per boards/freescale/<board>/tlb.c
+       Location   : cpu_init_early_f --> init_tlbs()
+       Properties : ..., AS0, ...
+      Note: It can overwrites previous TLB Entries
+
+   10) Disable TLB Entries of AS1
+       Location   : cpu_init_f --> disable_tlb()
+       Disable    : 15, 14
+
+   11) Create DDR's TLB entriy
+       Location   : Board_init_f -> init_func_ram -> initdram
+       TLB entry  : Search free TLB entry
+
+   12) Update Flash's TLB entry
+       Location   : Board_init_r
+       TLB entry  : Search from TLB entries
+       EPN -->RPN : CONFIG_SYS_FLASH_BASE --> CONFIG_SYS_FLASH_BASE_PHYS
+       Properties : Board specific size, AS0, I, G, IPROT