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

[Daniel P . Berrangé]

On Wed, Jul 31, 2024 at 06:52:35PM +0530, 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>
> 
> ---
> 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");

Check whether append is actually set, and report an fatal error in
that case. 

>  
> -    /* 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';
> +        }

Preferrable to use g_file_get_contents()

> +    } 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));
> -- 
> 2.45.2
> 
> 

With regards,
Daniel
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