x86: Add some documentation on how to port U-Boot on x86

Some information has been gleaned on tools and procedures for porting U-Boot to different x86 platforms. Add a few notes to start things off. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

x86: Add some documentation on how to port U-Boot on x86
Some information has been gleaned on tools and procedures for porting U-Boot to different x86 platforms. Add a few notes to start things off. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Simon Glass
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doc/README.x86
@@ -164,6 +164,70 @@
 	 mode to use. U-Boot sets up some reasonable values but you can
 	 adjust then with this command.
  
+Development Flow
+----------------
+
+These notes are for those who want to port U-Boot to a new x86 platform.
+
+Since x86 CPUs boot from SPI flash, a SPI flash emulator is a good investment.
+The Dediprog em100 can be used on Linux. The em100 tool is available here:
+
+   http://review.coreboot.org/p/em100.git
+
+On Minnowboard Max the following command line can be used:
+
+   sudo em100 -s -p LOW -d u-boot.rom -c W25Q64DW -r
+
+A suitable clip for connecting over the SPI flash chip is here:
+
+   http://www.dediprog.com/pd/programmer-accessories/EM-TC-8
+
+This allows you to override the SPI flash contents for development purposes.
+Typically you can write to the em100 in around 1200ms, considerably faster
+than programming the real flash device each time. The only important
+limitation of the em100 is that it only supports SPI bus speeds up to 20MHz.
+This means that images must be set to boot with that speed. This is an
+Intel-specific feature - e.g. tools/ifttool has an option to set the SPI
+speed in the SPI descriptor region.
+
+If your chip/board uses an Intel Firmware Support Package (FSP) it is fairly
+easy to fit it in. You can follow the Minnowboard Max implementation, for
+example. Hopefully you will just need to create new files similar to those
+in arch/x86/cpu/baytrail which provide Bay Trail support.
+
+If you are not using an FSP you have more freedom and more responsibility.
+The ivybridge support works this way, although it still uses a ROM for
+graphics and still has binary blobs containing Intel code. You should aim to
+support all important peripherals on your platform including video and storage.
+Use the device tree for configuration where possible.
+
+For the microcode you can create a suitable device tree file using the
+microcode tool:
+
+  ./tools/microcode-tool -d microcode.dat create <model>
+
+or if you only have header files and not the full Intel microcode.dat database:
+
+  ./tools/microcode-tool -H BAY_TRAIL_FSP_KIT/Microcode/M0130673322.h \
+	-H BAY_TRAIL_FSP_KIT/Microcode/M0130679901.h \
+	create all
+
+These are written to arch/x86/dts/microcode/ by default.
+
+Note that it is possible to just add the micrcode for your CPU if you know its
+model. U-Boot prints this information when it starts
+
+   CPU: x86_64, vendor Intel, device 30673h
+
+so here we can use the M0130673322 file.
+
+If you platform can display POST codes on two little 7-segment displays on
+the board, then you can use post_code() calls from C or assembler to monitor
+boot progress. This can be good for debugging.
+
+If not, you can try to get serial working as early as possible. The early
+debug serial port may be useful here. See setup_early_uart() for an example.
+
 TODO List
 ---------
 - Audio
...	...	@@ -164,6 +164,70 @@
164	164	mode to use. U-Boot sets up some reasonable values but you can
165	165	adjust then with this command.
166	166
	167	+Development Flow
	168	+----------------
	169	+
	170	+These notes are for those who want to port U-Boot to a new x86 platform.
	171	+
	172	+Since x86 CPUs boot from SPI flash, a SPI flash emulator is a good investment.
	173	+The Dediprog em100 can be used on Linux. The em100 tool is available here:
	174	+
	175	+ http://review.coreboot.org/p/em100.git
	176	+
	177	+On Minnowboard Max the following command line can be used:
	178	+
	179	+ sudo em100 -s -p LOW -d u-boot.rom -c W25Q64DW -r
	180	+
	181	+A suitable clip for connecting over the SPI flash chip is here:
	182	+
	183	+ http://www.dediprog.com/pd/programmer-accessories/EM-TC-8
	184	+
	185	+This allows you to override the SPI flash contents for development purposes.
	186	+Typically you can write to the em100 in around 1200ms, considerably faster
	187	+than programming the real flash device each time. The only important
	188	+limitation of the em100 is that it only supports SPI bus speeds up to 20MHz.
	189	+This means that images must be set to boot with that speed. This is an
	190	+Intel-specific feature - e.g. tools/ifttool has an option to set the SPI
	191	+speed in the SPI descriptor region.
	192	+
	193	+If your chip/board uses an Intel Firmware Support Package (FSP) it is fairly
	194	+easy to fit it in. You can follow the Minnowboard Max implementation, for
	195	+example. Hopefully you will just need to create new files similar to those
	196	+in arch/x86/cpu/baytrail which provide Bay Trail support.
	197	+
	198	+If you are not using an FSP you have more freedom and more responsibility.
	199	+The ivybridge support works this way, although it still uses a ROM for
	200	+graphics and still has binary blobs containing Intel code. You should aim to
	201	+support all important peripherals on your platform including video and storage.
	202	+Use the device tree for configuration where possible.
	203	+
	204	+For the microcode you can create a suitable device tree file using the
	205	+microcode tool:
	206	+
	207	+ ./tools/microcode-tool -d microcode.dat create <model>
	208	+
	209	+or if you only have header files and not the full Intel microcode.dat database:
	210	+
	211	+ ./tools/microcode-tool -H BAY_TRAIL_FSP_KIT/Microcode/M0130673322.h \
	212	+ -H BAY_TRAIL_FSP_KIT/Microcode/M0130679901.h \
	213	+ create all
	214	+
	215	+These are written to arch/x86/dts/microcode/ by default.
	216	+
	217	+Note that it is possible to just add the micrcode for your CPU if you know its
	218	+model. U-Boot prints this information when it starts
	219	+
	220	+ CPU: x86_64, vendor Intel, device 30673h
	221	+
	222	+so here we can use the M0130673322 file.
	223	+
	224	+If you platform can display POST codes on two little 7-segment displays on
	225	+the board, then you can use post_code() calls from C or assembler to monitor
	226	+boot progress. This can be good for debugging.
	227	+
	228	+If not, you can try to get serial working as early as possible. The early
	229	+debug serial port may be useful here. See setup_early_uart() for an example.
	230	+
167	231	TODO List
168	232	---------
169	233	- Audio