> On 25 Mar 2018, at 14:56, Pankaj Bansal <pankaj.bansal@xxxxxxx> wrote:
>
> Bootloader may need to fixup the device tree before OS can use it.
> e.g. a UEFI/DXE driver that has initialized a controller can add
> controller's clock frequency in controller node. This way OS need not to
> call get/set clock for that controller.
>
> Therefore, install fdt used by OS in configuration tables and associate it
> with device tree guid.
>
The firmware should be providing the dtb in the first place. On a uefi system, you should not use the dtbs shipped with the kernel, or use the dtb= command line parameter.
This may sound overly strict, but it is the only maintainable way: the dt bindings are the contract between firmware and os, and the os shipped dtbs essentially implement the platform side of the contract, pushing the firmware-os boundary down to a layer that is entirely unstandardized. Exposing the bundled dtb to the firmware is fragile, since the firmware has no guarantees whatsoever about its contents. (dt bindings are [supposed to be] backward compatible, but the device trees themselves are not)
So please find another way to solve this, and move away from dtb=
> UEFI/DXE drivers can fixup this device tree in their respective
> ExitBootServices events.
>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: linux-efi@xxxxxxxxxxxxxxx
> Signed-off-by: Pankaj Bansal <pankaj.bansal@xxxxxxx>
> ---
> drivers/firmware/efi/libstub/fdt.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
> index 177654e..df862e6 100644
> --- a/drivers/firmware/efi/libstub/fdt.c
> +++ b/drivers/firmware/efi/libstub/fdt.c
> @@ -265,6 +265,7 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table_arg,
> int runtime_entry_count = 0;
> struct efi_boot_memmap map;
> struct exit_boot_struct priv;
> + efi_guid_t fdt_guid = DEVICE_TREE_GUID;
>
> map.map = &runtime_map;
> map.map_size = &map_size;
> @@ -314,6 +315,13 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table_arg,
> goto fail_free_new_fdt;
> }
>
> + status = efi_call_early(install_configuration_table, &fdt_guid,
> + (void *)*new_fdt_addr);
> + if (status != EFI_SUCCESS) {
> + pr_efi_err(sys_table_arg, "Unable to install new device tree.\n");
> + goto fail_free_new_fdt;
> + }
> +
> priv.runtime_map = runtime_map;
> priv.runtime_entry_count = &runtime_entry_count;
> priv.new_fdt_addr = (void *)*new_fdt_addr;
> --
> 2.7.4
>
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