Commit 448719c5 authored by Bin Meng's avatar Bin Meng Committed by Simon Glass

x86: doc: Document some porting hints about Intel Quark

Document porting considerations for Intel Quark based board,
including MRC parameters and PCIe initialization.
Signed-off-by: default avatarBin Meng <bmeng.cn@gmail.com>
Acked-by: default avatarSimon Glass <sjg@chromium.org>
parent 5bf0f7f6
......@@ -733,6 +733,30 @@ Example output:
PCI_BDF(0, 3, 0) INTA PIRQA
...
Porting Hints
-------------
Quark-specific considerations:
To port U-Boot to other boards based on the Intel Quark SoC, a few things need
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 the 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 they are 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 a 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 they are implemented by the Intel
Galileo board support codes in board/intel/galileo/galileo.c.
TODO List
---------
- Audio
......
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