Re: [PATCH v2 1/2] arm/efi: Introduce uefi,cfg-load DT property

[Luca Fancellu <luca.fancellu@xxxxxxx>]

> On 22 Sep 2021, at 22:19, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> 
> On Wed, 22 Sep 2021, Luca Fancellu wrote:
>> Introduce the uefi,cfg-load DT property of /chosen
>> node for ARM whose presence decide whether to force
>> the load of the UEFI Xen configuration file.
>> 
>> The logic is that if any multiboot,module is found in
>> the DT, then the uefi,cfg-load property is used to see
>> if the UEFI Xen configuration file is needed.
>> 
>> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> 
> The patch looks OK, just a couple of minor comments below.
> 
> 
>> ---
>> v2 changes:
>> - Introduced uefi,cfg-load property
>> - Add documentation about the property
>> ---
>> docs/misc/efi.pandoc        |  2 ++
>> xen/arch/arm/efi/efi-boot.h | 28 +++++++++++++++++++++++-----
>> 2 files changed, 25 insertions(+), 5 deletions(-)
>> 
>> diff --git a/docs/misc/efi.pandoc b/docs/misc/efi.pandoc
>> index ac3cd58cae..e289c5e7ba 100644
>> --- a/docs/misc/efi.pandoc
>> +++ b/docs/misc/efi.pandoc
>> @@ -14,6 +14,8 @@ loaded the modules and describes them in the device tree 
>> provided to Xen.  If a
>> bootloader provides a device tree containing modules then any configuration
>> files are ignored, and the bootloader is responsible for populating all
>> relevant device tree nodes.
>> +The property "uefi,cfg-load" can be specified in the /chosen node to force 
>> Xen
>> +to load the configuration file even if multiboot modules are found.
> 

Hi Stefano,

> I think that, in addition to this, we also need to add the property to
> docs/misc/arm/device-tree/booting.txt where our "official" device tree
> bindings are maintained. I would add it below "Command lines" and before
> "Creating Multiple Domains directly from Xen" maybe as a new chapter.
> It could be called "Other Options" but other ideas could be valid too.
> 
> You can say that uefi,cfg-load is a boolean.

Sure, I will add in v3, what about this:

UEFI boot and DT
==============

When Xen is booted using UEFI, it doesn't read the configuration file if any
multiboot module is specified. To force Xen to load the configuration file, the
boolean property uefi,cfg-load must be declared in the /chosen node.

> 
>> Once built, `make install-xen` will place the resulting binary directly into
>> the EFI boot partition, provided `EFI_VENDOR` is set in the environment (and
>> diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
>> index cf9c37153f..8ceeba4ad1 100644
>> --- a/xen/arch/arm/efi/efi-boot.h
>> +++ b/xen/arch/arm/efi/efi-boot.h
>> @@ -581,22 +581,40 @@ static void __init 
>> efi_arch_load_addr_check(EFI_LOADED_IMAGE *loaded_image)
>> 
>> static bool __init efi_arch_use_config_file(EFI_SYSTEM_TABLE *SystemTable)
>> {
>> +    bool skip_cfg_file = false;
>>     /*
>>      * For arm, we may get a device tree from GRUB (or other bootloader)
>>      * that contains modules that have already been loaded into memory.  In
>> -     * this case, we do not use a configuration file, and rely on the
>> -     * bootloader to have loaded all required modules and appropriate
>> -     * options.
>> +     * this case, we search for the property uefi,cfg-load in the /chosen 
>> node
>> +     * to decide whether to skip the UEFI Xen configuration file or not.
>>      */
>> 
>>     fdt = lookup_fdt_config_table(SystemTable);
>>     dtbfile.ptr = fdt;
>>     dtbfile.need_to_free = false; /* Config table memory can't be freed. */
>> -    if ( !fdt || fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") 
>> < 0 )
>> +
>> +    if ( fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") > 0 )
>> +    {
>> +        /* Locate chosen node */
>> +        int node = fdt_subnode_offset(fdt, 0, "chosen");
>> +        const void *cfg_load_prop;
>> +        int cfg_load_len;
>> +
>> +        if ( node > 0 )
>> +        {
>> +            /* Check if uefi,cfg-load property exists */
>> +            cfg_load_prop = fdt_getprop(fdt, node, "uefi,cfg-load",
>> +                                        &cfg_load_len);
>> +            if ( !cfg_load_prop )
>> +                skip_cfg_file = true;
>> +        }
>> +    }
>> +
>> +    if ( !fdt || !skip_cfg_file )
> 
> Just a suggestion, but rather than the double negative, wouldn't it be
> simpler to define it as
> 
>    bool load_cfg_file = true;
> 
> ?

Sure I will modify it.

> 
> 
>>     {
>>         /*
>>          * We either have no FDT, or one without modules, so we must have a
>> -         * Xen EFI configuration file to specify modules.  (dom0 required)
>> +         * Xen EFI configuration file to specify modules.
>>          */
> 
> Also mention in the commit message that you are taking the opportunity
> to update this comment do remove "dom0 required".

Yes I will add it in the commit message

Cheers,
Luca

> 
> 
>>         return true;
>>     }
>> -- 
>> 2.17.1