[U-Boot] [PATCH] arm: Add support for semihosting for armv8 fastmodel targets.

[Tom Rini]

On Wed, Mar 12, 2014 at 09:04:01AM -0700, Darwin Rambo wrote:

> The reason for this change is to be able to use the ARM Trusted Firmware
> (ATF) to load the various ATF images, plus u-boot, which can then load
> the kernel/ramdisk/dtb with calls to an external host from a standard
> fastmodel armv8 board file using semihosting, and then launch the kernel
> without a bootwrapper. This gives us a more realistic boot sequence.
> 
> Rather than create a new armv8 board similar to armltd/vexpress64, add
> semihosting calls to the existing one, enabled with CONFIG_SEMIHOSTING.
> Also add a new board config file vexpress_aemv8a_semi.h. This change is
> tested and works on the ARM foundation model.
> 
> Support for armv7 in fastmodel is less useful due to the wide range of
> available silicon but this change contains an untested armv7 placeholder
> if desired.
> 
> The level of semihosting support is minimal, restricted to just what it
> takes to load images to memory. If more semihosting functionality is
> required, such as file seek, outputting strings, reading characters, etc,
> then it can be easily added later.
> 
> Signed-off-by: Darwin Rambo <drambo at broadcom.com>

At the high-level, I'm fine with this.  But as an implementation detail
we need to either leverage vexpress_common.h or create a
vexpress_arm64_common.h or something.  There's a lot in common between
these two configs, and some further clean-up we need to do to the first
one anyhow.

Next:
> +#ifdef CONFIG_BOARD_LATE_INIT
> +int board_late_init(void)
> +{
> +#ifdef CONFIG_SEMIHOSTING
> +
> +	/*
> +	 * We require that the board include file defines these env variables:
> +	 * - kernel_addr
> +	 * - initrd_addr
> +	 * - fdt_addr
> +	 *
> +	 * For the "fdt chosen" startup macro, this code will then define:
> +	 * - initrd_end (based on initrd_base plus actual initrd_size)
> +	 *
> +	 * We will then load the kernel, initrd, and fdt into the specified
> +	 * locations in memory in a similar way that the ATF fastmodel code
> +	 * uses semihosting calls to load other boot stages and u-boot itself.
> +	 */
> +
> +	/* Env variable strings */
> +	char *kernel_addr_str = getenv("kernel_addr");
> +	char *initrd_addr_str = getenv("initrd_addr");
> +	char *fdt_addr_str = getenv("fdt_addr");
> +	char initrd_end_str[64];

First, we need to document this stuff in a README file as well.  Second,
I'd like to see kernel_addr_r / ramdisk_addr_r / fdt_addr_r used to
match-up with what Dennis Gilmore has been working on to get a common
env working.

[snip]
> +	/* Assumes kernel is lower in memory than fdt */
> +	smh_load(CONFIG_KNLNAME, kernel_addr, fdt_addr - kernel_addr, 1);
> +
> +	/* Load fdt to memory */
> +	smh_load(CONFIG_FDTNAME, fdt_addr, 0x20000, 1);
> +
> +	/* Load initrd to memory */
> +	smh_load(CONFIG_RDNAME, initrd_addr, initrd_size, 1);

Is there a reason we can't also get these from the environment?  Or a
limitation of (how we support) the simulator that we don't have
persistent r/w environment right now?

Thanks!

-- 
Tom
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