Re: [PATCH v1] board: mpfs_icicle: implement board_fdt_blob_setup()

[Conor Dooley <conor@kernel.org>]

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On Tue, Jun 25, 2024 at 10:08:06AM +0100, Conor Dooley wrote:
> The firmware on the Icicle is capable of providing a devicetree in a1 to
> U-Boot, but until now the devicetree has been packaged in a "payload" [1]
> alongside U-Boot (or other bootloaders/RTOSes) and appended to the image.
> The address of this appended devicetree is placed in a1 by the firmware.
> This meant that the mechanism used by OF_SEPARATE to locate the
> devicetree at the end of the image would pick up the one provided by the
> firmware when u-boot-nodtb.bin was in the payload and U-Boot's devicetree
> when u-boot.bin was.
> 
> The firmware is now going to be capable of providing a minimal devicetree
> (quite cut down due to severe space constraints), but this devicetree is
> linked into the firmware that runs out of the L2 rather than at the end
> of the U-Boot image. Implement board_fdt_blob_setup() so that this
> devicetree can be optionally used, and the devicetree provided in the
> "payload" can be used without relying on "happening" to implement the
> same strategy as OF_SEPARATE expects in combination with
> u-boot-nodtb.bin. Unlike other RISC-V boards, the firmware provided
> devicetree is only used when OF_BOARD is set, so that the almost
> certainly more complete devicetree in U-Boot will be used unless
> explicitly requested otherwise.
> 
> Link: https://github.com/polarfire-soc/hart-software-services/blob/master/tools/hss-payload-generator/README.md [1]
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Off-list it was suggested to me to use MULTI_DTB_FIT in addition what
what I've done here, to allow U-Boot to actually make use of the
information in the firmware provided dtb to select a more complete dtb
for the OS (or for itself). I whipped up the following quickly just to
test that it works, but was super lazy about it as you can see:
diff --git a/board/microchip/mpfs_icicle/mpfs_icicle.c b/board/microchip/mpfs_icicle/mpfs_icicle.c
index ade150bec98..76f37a7199c 100644
--- a/board/microchip/mpfs_icicle/mpfs_icicle.c
+++ b/board/microchip/mpfs_icicle/mpfs_icicle.c
@@ -52,6 +52,31 @@ static void read_device_serial_number(u8 *response, u8 response_size)
 		response_buf[idx] = readb(MPFS_SYS_SERVICE_MAILBOX + idx);
 }
 
+#ifdef CONFIG_MULTI_DTB_FIT
+int board_fit_config_name_match(const char *name)
+{
+
+	char compat[256] = "microchip,";
+	size_t max = 256 - strlen("microchip,");
+	int ret;
+
+	/*
+	 * If there's not a HSS provided dtb, there's no point re-selecting
+	 * since we'd just end up re-selecting the same dtb again.
+	 */
+	if (!gd->arch.firmware_fdt_addr)
+		return -EINVAL;
+
+	strncat(compat, name, max);
+	ret = fdt_node_check_compatible((void *)gd->arch.firmware_fdt_addr, 0, compat);
+	if (ret)
+		return -EINVAL;
+
+	debug("found a match for compat: %s\n", compat);
+	return 0;
+}
+#endif
+
 void *board_fdt_blob_setup(int *err)
 {
 	*err = 0;

I'd rather invert the logic so that we compare the name of the config
with the compatible strings sans vendor prefix - what's here would work
for any of the boards were we are the vendor but not for the
beaglev-fire. Granted that board is not supported in U-Boot right now,
but I'll probably accompany a v2 of this that with an OF_UPSTREAM
conversion for the PolarFire SoC boards.

However, I don't really understand how I could make my implementation of
board_fdt_blob_setup() play nicely. It appears that if I enable OF_BOARD
then then the multi dtb stuff never kicks in (since we've updated the
fdt pointer to that of the firmware provided dtb). Given that
setup_multi_dtb_fit() is called almost immediately after
board_fdt_blob_setup() in fdtdec_setup(), it seems like dropping
board_fdt_blob_setup() entirely might be a better approach?

I think that'll have the same behaviours we want w.r.t. firmware config
options etc - except U-Boot will have to be built with functional
devicetrees for all boards it wants to support. Maybe that's not a
problem since it'd still be a single build for all boards. Maybe
Heinrich has a better opinion there than I do..

Thanks,
Conor.


> ---
> CC: Ivan Griffin <ivan.griffin@microchip.com>
> CC: Padmarao Begari <padmarao.begari@microchip.com>
> CC: Cyril Jean <cyril.jean@microchip.com>
> CC: Tom Rini <trini@konsulko.com>
> CC: Conor Dooley <conor.dooley@microchip.com>
> CC: u-boot@lists.denx.de
> ---
>  board/microchip/mpfs_icicle/mpfs_icicle.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/board/microchip/mpfs_icicle/mpfs_icicle.c b/board/microchip/mpfs_icicle/mpfs_icicle.c
> index 4d7d843dfa3..2c1f7175f0e 100644
> --- a/board/microchip/mpfs_icicle/mpfs_icicle.c
> +++ b/board/microchip/mpfs_icicle/mpfs_icicle.c
> @@ -9,6 +9,7 @@
>  #include <init.h>
>  #include <asm/global_data.h>
>  #include <asm/io.h>
> +#include <asm/sections.h>
>  
>  DECLARE_GLOBAL_DATA_PTR;
>  
> @@ -50,6 +51,24 @@ static void read_device_serial_number(u8 *response, u8 response_size)
>  		response_buf[idx] = readb(MPFS_SYS_SERVICE_MAILBOX + idx);
>  }
>  
> +void *board_fdt_blob_setup(int *err)
> +{
> +	*err = 0;
> +	/*
> +	 * The devicetree provided by the previous stage is very minimal due to
> +	 * severe space constraints. The firmware performs no fixups etc.
> +	 * U-Boot, if providing a devicetree, almost certainly has a better
> +	 * more complete one than the firmware so that provided by the firmware
> +	 * is ignored for OF_SEPARATE.
> +	 */
> +	if (IS_ENABLED(CONFIG_OF_BOARD)) {
> +		if (gd->arch.firmware_fdt_addr)
> +			return (ulong *)(uintptr_t)gd->arch.firmware_fdt_addr;
> +	}
> +
> +	return (ulong *)_end;
> +}
> +
>  int board_init(void)
>  {
>  	/* For now nothing to do here. */
> -- 
> 2.43.2
> 

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