Re: [RFC PATCH] hw/ppc: Implement -dtb support for PowerNV

[Cédric Le Goater]

Hello Aditya,

On 7/31/24 15:22, Aditya Gupta wrote:
> Currently any device tree passed with -dtb option in QEMU, was ignored
> by the PowerNV code.
>
> Read and pass the passed -dtb to the kernel, thus enabling easier
> debugging with custom DTBs.

I thought we had enough controls with the QEMU command line options to
generate a custom DTB. We should improve that first. Unless you want
to mimic a bogus DTB as generated by hostboot and check skiboot behavior.

Can you explain more the use case please ? Is it for skiboot testing ?

Thanks,

C.


> The existing behaviour when -dtb is 'not' passed, is preserved as-is.
>
> But when a '-dtb' is passed, it completely overrides any dtb nodes or
> changes QEMU might have done, such as '-append' arguments to the kernel
> (which are mentioned in /chosen/bootargs in the dtb), hence add warning
> when -dtb is being used
>
> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>
> ---
> This is an RFC patch, and hence might not be the final implementation,
> though this current one is a solution which works
>
> ---
>   hw/ppc/pnv.c | 29 ++++++++++++++++++++++++++---
>   1 file changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index 3526852685b4..12cc909b9e26 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -714,6 +714,8 @@ static void pnv_reset(MachineState *machine, ShutdownCause 
> reason)
>       PnvMachineState *pnv = PNV_MACHINE(machine);
>       IPMIBmc *bmc;
>       void *fdt;
> +    FILE *fdt_file;
> +    uint32_t fdt_size;
>   
>       qemu_devices_reset(reason);
>   
> @@ -736,10 +738,31 @@ static void pnv_reset(MachineState *machine, ShutdownCause reason)
>           }
>       }
>   
> -    fdt = pnv_dt_create(machine);
> +    if (machine->dtb) {
> +        warn_report("with manually passed dtb, some options like '-append'"
> +                " might ignored and the dtb passed will be used as-is");
>   
> -    /* Pack resulting tree */
> -    _FDT((fdt_pack(fdt)));
> +        fdt = g_malloc0(FDT_MAX_SIZE);
> +
> +        /* read the file 'machine->dtb', and load it into 'fdt' buffer */
> +        fdt_file = fopen(machine->dtb, "r");
> +        if (fdt_file != NULL) {
> +            fdt_size = fread(fdt, sizeof(char), FDT_MAX_SIZE, fdt_file);
> +            if (ferror(fdt_file) != 0) {
> +                error_report("Could not load dtb '%s'",
> +                             machine->dtb);
> +                exit(1);
> +            }
> +
> +            /* mark end of the fdt buffer with '\0' */
> +            ((char *)fdt)[fdt_size] = '\0';
> +        }
> +    } else {
> +        fdt = pnv_dt_create(machine);
> +
> +        /* Pack resulting tree */
> +        _FDT((fdt_pack(fdt)));
> +    }
>   
>       qemu_fdt_dumpdtb(fdt, fdt_totalsize(fdt));
>       cpu_physical_memory_write(PNV_FDT_ADDR, fdt, fdt_totalsize(fdt));