Re: xen/arm: How to hide console UART from dom0?

[Julien Grall <julien.grall@citrix.com>]

On 05/31/2013 12:07 PM, Ian Campbell wrote:

> Current mainline Xen crashes for me during dom0 boot because the console
> UART is exposed to dom0 in the DTB and nothing is mapped there, which
> causes it to fault trying to access it.
> 
> My, unsuitable for upstream, local hack is:
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 0abacda..5d4916c 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -231,6 +231,7 @@ static int fdt_next_dom0_node(const void *fdt, int node,
>                                int *depth_out)
>  {
>      int depth = *depth_out;
> +    const char *name;
>  
>      while ( (node = fdt_next_node(fdt, node, &depth)) &&
>              node >= 0 && depth >= 0 )
> @@ -250,7 +251,16 @@ static int fdt_next_dom0_node(const void *fdt, int node,
>                                         "xen,multiboot-module" ) == 0 )
>              continue;
>  
> +        name = fdt_get_name(fdt, node, NULL);
> +        if (!strcmp(name, "uart@0c0000"))
> +        {
> +            printk("Skipping %s\n", name);
> +            continue;
> +        }
> +
>          /* We've arrived at a node which dom0 is interested in. */
> +        printk("Node %s to dom0\n", name);
> +
>          break;
>      }
>  
> I tried seeing if I could remember the name of the console DT device but
> in dt_uart_init I get:
>         dt_node_full_name
>         => /smb/motherboard/iofpga@3,00000000/uart@0c000
>         dt_node_name => uart
> Neither of which match the required "uart@0c000" which
> fdt_next_dom0_node has in its hand.

By default, the part after @ is removed. If needed, it's easily to
provide a pointer to "uart@0c000" but I'm not sure it's usefull for us.

> Julien, I know you have longer term plans to create dom0's device tree
> from Xen's unflattened device tree using the used_by field but I suppose
> that won't be happening for 4.3 at this stage? Is there a better short
> term hack we can make here? How do you work around this issue?


Right. It's possible to add a property: status = "disabled"; on the
specific node (here the UART). Linux will interpret this property and
won't use the node.
For the moment, this property is not used by Xen so you can directly add
it on your DTS.

-- 
Julien