Document porting considerations for Intel Quark based board, including MRC parameters and PCIe initialization.
Signed-off-by: Bin Meng bmeng.cn@gmail.com
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doc/README.x86 | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
diff --git a/doc/README.x86 b/doc/README.x86 index 5f9c46f..f76db7f 100644 --- a/doc/README.x86 +++ b/doc/README.x86 @@ -733,6 +733,29 @@ Example output: PCI_BDF(0, 3, 0) INTA PIRQA ...
+Porting Hints +------------- + +Quark-specific considerations: + +To port U-Boot on other Intel Quark SoC based board, something needs to be taken +care of. The first important part is the Memory Reference Code (MRC) parameters. +Quark MRC supports memory-down configuration only. All these MRC parameters are +supplied via board device tree. To get started, first copy the MRC section of +arch/x86/dts/galileo.dts to your board's device tree, then change these values +by consulting board manuals or your hardware vendor. Available MRC parameter +values are listed in include/dt-bindings/mrc/quark.h. The other tricky part is +with PCIe. Quark SoC integrates two PCIe root ports, but by default it is held +in reset after power on. In U-Boot, PCIe initialization is properly handled as +per Quark's firmware writer guide. In your board support codes, you need provide +two routines to aid PCIe initialization, which are: board_assert_perst() and +board_deassert_perst(). The two routines need implement board-specific mechanism +to assert/deassert PCIe PERST# pin. Care must be taken that in those routines +that any APIs that may trigger PCI enumeration process are strictly forbidden, +as any access to PCIe root port's configuration registers will cause system hang +while it is held in reset. For more details, check how it is implemented by the +Intel Galileo board supported codes in board/intel/galileo/galileo.c. + TODO List --------- - Audio