Re: [PATCH v2 3/9] riscv: Add SOC early init support

[Sean Anderson <seanga2@gmail.com>]

On 3/12/20 1:11 AM, Damien Le Moal wrote:
> Add a mechanism for early SoC initialization for platforms that need
> additional hardware initialization not possible through the regular
> device tree and drivers mechanism. With this, a SoC specific
> initialization function can be called very early, before DTB parsing
> is done by parse_dtb() in Linux RISC-V kernel setup code.

Why does it need to be called that early (e.g. before parsing dtb)?

> 
> This can be very useful for early hardware initialization for No-MMU
> kernels booted directly in M-mode because it is quite likely that no
> other booting stage exist prior to the No-MMU kernel.
> 
> Example use of a SoC early initialization is as follows:
> 
> static void vendor_abc_early_init(const void *fdt)
> {
> 	/*
> 	 * some early init code here that can use simple matches
> 	 * against the flat device tree file.
> 	 */
> }
> SOC_EARLY_INIT_DECLARE("vendor,abc", abc_early_init);
> 
> This early initialization function is executed only if the flat device
> tree for the board has a 'compatible = "vendor,abc"' entry;
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>

--Sean