Re: [PATCH v2] hw/ppc: Implement -dtb support for PowerNV

[Cédric Le Goater]

On 8/1/24 10:51, 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.
>
> 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>
>
> ---
> Changelog
> ===========
> v2:
>   + move reading dtb and warning to pnv_init
>
> v1:
>   + use 'g_file_get_contents' and add check for -append & -dtb as suggested by 
> Daniel
> ---
> ---
>   hw/ppc/pnv.c         | 29 ++++++++++++++++++++++++++---
>   include/hw/ppc/pnv.h |  2 ++
>   2 files changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index 3526852685b4..047725bd97fc 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -736,11 +736,14 @@ static void pnv_reset(MachineState *machine, 
> ShutdownCause reason)
>           }
>       }
>   
> -    fdt = pnv_dt_create(machine);
> +    if (!pnv->fdt) {
> +        pnv->fdt = pnv_dt_create(machine);

At next reset, the dtb specified on the command line will be ignored.
Please reverse the logic :

    if (pnv->fdt) {
        fdt = pnv->fdt;
    } else {
        fdt = pnv_dt_create(machine);
        /* Pack resulting tree */
        _FDT((fdt_pack(fdt)));
    }

but, at the end of pnv_reset(), beware of :

    g_free(machine->fdt);
    machine->fdt = fdt;


> -    /* Pack resulting tree */
> -    _FDT((fdt_pack(fdt)));
> +        /* Pack resulting tree */
> +        _FDT((fdt_pack(pnv->fdt)));
> +    }
>   
> +    fdt = pnv->fdt;
>       qemu_fdt_dumpdtb(fdt, fdt_totalsize(fdt));
>       cpu_physical_memory_write(PNV_FDT_ADDR, fdt, fdt_totalsize(fdt));
>   
> @@ -952,6 +955,14 @@ static void pnv_init(MachineState *machine)
>           g_free(sz);
>           exit(EXIT_FAILURE);
>       }
> +
> +    /* checks for invalid option combinations */
> +    if (machine->dtb && (strlen(machine->kernel_cmdline) != 0)) {
> +        error_report("-append and -dtb cannot be used together, as passed"
> +                " command line is ignored in case of custom dtb");
> +        exit(EXIT_FAILURE);

I think this is redundant with the warn report below.

> +    }
> +
>       memory_region_add_subregion(get_system_memory(), 0, machine->ram);
>   
>       /*
> @@ -1003,6 +1014,18 @@ static void pnv_init(MachineState *machine)
>           }
>       }
>   
> +    /* load dtb if passed */
> +    if (machine->dtb) {
> +        warn_report("with manually passed dtb, some options like '-append'"
> +                " will get ignored and the dtb passed will be used as-is");
> +
> +        /* read the file 'machine->dtb', and load it into 'fdt' buffer */
> +        if (!g_file_get_contents(machine->dtb, (gchar **)&pnv->fdt, NULL, 
> NULL)) {
> +            error_report("Could not load dtb '%s'", machine->dtb);
> +            exit(1);
> +        }

There is a load_device_tree() routine you could use. Please check how other
machines handle -dtb for examples.


Thanks,

C.



> +    }
> +
>       /* MSIs are supported on this platform */
>       msi_nonbroken = true;
>   
> diff --git a/include/hw/ppc/pnv.h b/include/hw/ppc/pnv.h
> index fcb6699150c8..20b68fd9264e 100644
> --- a/include/hw/ppc/pnv.h
> +++ b/include/hw/ppc/pnv.h
> @@ -91,6 +91,8 @@ struct PnvMachineState {
>       uint32_t     initrd_base;
>       long         initrd_size;
>   
> +    void         *fdt;
> +
>       uint32_t     num_chips;
>       PnvChip      **chips;
>