From: Bin Meng Date: Thu, 10 Sep 2015 06:20:29 +0000 (-0700) Subject: x86: doc: Document some porting hints about Intel Quark X-Git-Tag: v2015.10-rc4~25^2~2 X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=448719c5e7b572d6ec89e032ca5165897cabfbec;p=oweals%2Fu-boot.git 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: Bin Meng Acked-by: Simon Glass --- diff --git a/doc/README.x86 b/doc/README.x86 index 5f9c46f05d..d6b24ee75a 100644 --- a/doc/README.x86 +++ b/doc/README.x86 @@ -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