Re: [Qemu-devel] [PATCH] hw/i386: add device tree support

[Eduardo Habkost]

On Tue, Apr 05, 2016 at 07:11:28PM +0200, Antonio Borneo wrote:
> With "-dtb" on command-line:
> - append the device tree blob to the kernel image;
> - pass the blob's pointer to the kernel through setup_data, as
>   requested by upstream kernel commit da6b737b9ab7 ("x86: Add
>   device tree support").
> 
> The device tree blob is passed as-is to the guest; none of its
> fields is modified nor updated. This is not an issue; the kernel
> commit above uses the device tree only as an extension to the
> traditional kernel configuration.
> 
> To: "Michael S. Tsirkin" <address@hidden>
> To: Paolo Bonzini <address@hidden>
> To: Richard Henderson <address@hidden>
> To: Eduardo Habkost <address@hidden>
> Cc: address@hidden
> Cc: Sebastian Andrzej Siewior <address@hidden>
> Signed-off-by: Antonio Borneo <address@hidden>
> ---
> 
> Hi,
> 
> I'm not expert on the x86 memory map at boot and during kernel
> boot; I found easy to just append the dtb to the kernel image.
> From my tests this patch is working fine.
> If you have any hint for a different loading address for dtb, I
> would be glad to modify this code.

I was worried that changing FW_CFG_KERNEL_SIZE could break
something, but this seems to be OK because:

* The only user of FW_CFG_KERNEL_* seems to be 
  read_fw_blob_addr32(), used by linuxboot.S and multiboot.S just
  for reading data from fw_cfg into RAM;
* multiboot code already does something similar: it uses
  FW_CFG_KERNEL_SIZE not just for the kernel image size, but for
  the kernel image plus the extra data loaded after it.

One small comment below:

[...]
> @@ -989,6 +1006,35 @@ static void load_linux(PCMachineState *pcms,
>          exit(1);
>      }
>      fclose(f);
> +
> +    /* append dtb to kernel */
> +    if (dtb_filename) {
> +        if (protocol < 0x209) {
> +            fprintf(stderr, "qemu: Linux kernel too old to load a dtb\n");
> +            exit(1);
> +        }
> +
> +        dtb_size = get_image_size(dtb_filename);
> +        if (dtb_size <= 0) {
> +            fprintf(stderr, "qemu: error reading dtb %s: %s\n",
> +                    dtb_filename, strerror(errno));
> +            exit(1);
> +        }
> +
> +        setup_data_offset = QEMU_ALIGN_UP(kernel_size, 16);
> +        kernel_size = setup_data_offset + sizeof(struct setup_data) + 
> dtb_size;
> +        kernel = g_realloc(kernel, kernel_size);
> +
> +        stq_p(header+0x250, prot_addr + setup_data_offset);
> +
> +        setup_data = (struct setup_data *)(kernel + setup_data_offset);
> +        setup_data->next = 0;
> +        setup_data->type = cpu_to_le32(SETUP_DTB);
> +        setup_data->len = cpu_to_le32(dtb_size);
> +
> +        load_image(dtb_filename, setup_data->data);

load_image() is deprecated, please use
load_image_size(dtb_filename, setup_data->data, dtb_size)
instead.

> +    }
> +
>      memcpy(setup, header, MIN(sizeof(header), setup_size));
>  
>      fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, prot_addr);
> -- 
> 2.8.0
> 

-- 
Eduardo