[PATCH] of: fix phandle cache creation for DTs with no phandles

[Frank Rowand]

On 09/11/18 07:56, Rob Herring wrote:
> With commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of
> of_find_node_by_phandle()"), a G3 PowerMac fails to boot. The root cause
> is the DT for this system has no phandle properties when booted with
> BootX. of_populate_phandle_cache() does not handle the case of no
> phandles correctly. The problem is roundup_pow_of_two() for 0 is
> undefined. The implementation subtracts 1 underflowing and then things
> are in the weeds.
> 
> Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
> Cc: stable at vger.kernel.org # 4.17+
> Reported-by: Finn Thain <fthain at telegraphics.com.au>
> Tested-by: Stan Johnson <userm57 at yahoo.com>
> Cc: Frank Rowand <frowand.list at gmail.com>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Signed-off-by: Rob Herring <robh at kernel.org>
> ---
> Here's a formal patch of what Stan tested. Will send to Linus this week.
> 
> Rob
> 
>  drivers/of/base.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index a055cd1ef96d..17ae594b7014 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -140,6 +140,9 @@ void of_populate_phandle_cache(void)
>  		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
>  			phandles++;
>  
> +	if (!phandles)
> +		goto out;
> +
>  	cache_entries = roundup_pow_of_two(phandles);
>  	phandle_cache_mask = cache_entries - 1;
>  
> 


Reviewed-by: Frank Rowand <frank.rowand at sony.com>