[U-Boot-Users] Ideas on U-Boot configuration with FDT
wg at grandegger.com
Fri May 18 17:01:49 CEST 2007
Timur Tabi wrote:
> Wolfgang Grandegger wrote:
>>> I think fdt_checkboard() (or boardcheck) should be run from inside
>>> the fdt_open_into() command. This takes advantage of the existing
>>> mechanism of fdt_open_into() to return an error. It also allows for
>>> a device tree to be opened after U-Boot has booted.
>> But it's too late for initial initialization (before RAM is available).
> Just make it so that fdt_open_into() is called early:
> #if defined(CFG_FDT_ADDR_FLASH)
> #if defined(CONFIG_MISC_INIT_F)
> #if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
> and init_fdt() calls fdt_open_into().
RAM is _not_ available at that stage.
>> Using the FDT directly from ROM is not recommended because access
>> might be slow, but we likely need it for early initialization.
> I don't access speed is important for the reading the FDT, especially
> flash vs. RAM. It's not that much slower.
Depends, you might be right for FLASH on a 32-bit bus. On slow ROM
devices and slow processors, it matters.
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