[RFC] Raspberry Pi: copy /system/linux,{serial,revision} from firmware

[Fiona Klute]

Hi Peter, everyone,

do you have any comments? My main concern is if creating a temporary 
overlay is the right approach here, or if there's better way to create 
the /system node if needed.

Best regards,
Fiona

Am 15.02.25 um 14:01 schrieb Peter Robinson:
> Hi Fiona,
> 
> I'll review and test this the coming week and provide feedback.
> 
> On Tue, 11 Feb 2025 at 13:58, Fiona Klute <fiona.klute at gmx.de> wrote:
> 
>> Both the Raspberry Pi downstream kernel [1] and some userspace tools
>> [2] use the revision property to identify the board, and the latter
>> fails if it is absent. The firmware creates the /system node, so we
>> need to do the same.
>>
>> [1]
>> https://github.com/raspberrypi/linux/blob/0f292fbb6346b05766152902076895558ac23f9a/arch/arm/mach-bcm/board_bcm2835.c#L23-L33
>> [2]
>> https://github.com/jgarff/rpi_ws281x/blob/7fc0bf8b31d715bbecf28e852ede5aaa388180da/rpihw.c#L579
>>
>> Signed-off-by: Fiona Klute <fiona.klute at gmx.de>
>> Cc: Matthias Brugger <mbrugger at suse.com>
>> Cc: Peter Robinson <pbrobinson at gmail.com>
>> Cc: Tom Rini <trini at konsulko.com>
>> ---
>> I'm sending this as RFC because I'm not sure if creating a temporary
>> overlay is the best approach here, advice on a better way to create the
>> /system node if needed is very much welcome. I know I'll need to add
>> more error checks, I'll do that after I know I have the right approach.
>>
>>   board/raspberrypi/rpi/rpi.c | 37 +++++++++++++++++++++++++++++++++++++
>>   1 file changed, 37 insertions(+)
>>
>> diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
>> index aa39afa338a..647716127c7 100644
>> --- a/board/raspberrypi/rpi/rpi.c
>> +++ b/board/raspberrypi/rpi/rpi.c
>> @@ -550,6 +550,41 @@ int copy_property(void *dst, void *src, char *path,
>> char *property)
>>          return fdt_setprop(dst, dst_offset, property, prop, len);
>>   }
>>
>> +int copy_system_node(void *fdt, void *fw_fdt)
>> +{
>> +       const fdt32_t *prop;
>> +       char fdto[2048];
>> +       int src_offset;
>> +       int len;
>> +
>> +       src_offset = fdt_path_offset(fw_fdt, "/system");
>> +       if (src_offset < 0)
>> +               return -1;
>> +
>> +       fdt_create(fdto, sizeof(fdto));
>> +       fdt_finish_reservemap(fdto);
>> +       fdt_begin_node(fdto, "");
>> +       fdt_begin_node(fdto, "fragment");
>> +       fdt_property_string(fdto, "target-path", "/");
>> +       fdt_begin_node(fdto, "__overlay__");
>> +       fdt_begin_node(fdto, "system");
>> +
>> +       prop = fdt_getprop(fw_fdt, src_offset, "linux,serial", &len);
>> +       if (prop)
>> +               fdt_property(fdto, "linux,serial", prop, len);
>> +       prop = fdt_getprop(fw_fdt, src_offset, "linux,revision", &len);
>> +       if (prop)
>> +               fdt_property(fdto, "linux,revision", prop, len);
>> +
>> +       fdt_end_node(fdto);
>> +       fdt_end_node(fdto);
>> +       fdt_end_node(fdto);
>> +       fdt_end_node(fdto);
>> +       fdt_finish(fdto);
>> +
>> +       fdt_overlay_apply_verbose(fdt, fdto);
>> +}
>> +
>>   /* Copy tweaks from the firmware dtb to the loaded dtb */
>>   void  update_fdt_from_fw(void *fdt, void *fw_fdt)
>>   {
>> @@ -560,6 +595,8 @@ void  update_fdt_from_fw(void *fdt, void *fw_fdt)
>>          /* The firmware provides a more precise model; so copy that */
>>          copy_property(fdt, fw_fdt, "/", "model");
>>
>> +       copy_system_node(fdt, fw_fdt);
>> +
>>          /* memory reserve as suggested by the firmware */
>>          copy_property(fdt, fw_fdt, "/", "memreserve");
>>
>> --
>> 2.47.2
>>
>>