Subject: Re: [RFC 1/1] powerpc: legacy serial port use device tree cell-index property

From: Scott Wood <[email-masked]>
Date: Mon, 21 Dec 2015 21:42:11 -0600

On Wed, 2015-11-25 at 10:46 -0800, Curt Brune wrote:
> Currently for PowerPC systems using device tree, the legacy serial
> ports are allocated in the order by which they are found in the device
> tree structure.
> 
> This can cause problems in cases where the device tree nodes are
> sysnthesized by an external program (kexec for example), which may not
> preserve the original order of the device tree nodes.  This in turn
> can result in the serial console changing from ttyS0 to ttyS1
> unexpectedly.
> 
> This patch uses the 'cell-index' property (if present) to map UART
> device tree nodes to legacy serial port number.  The cell-index
> property is widely used in all the Freescale .dts files for PowerPC.
> 
> Signed-off-by: Curt Brune <[email-masked]>
> ---
>  arch/powerpc/kernel/legacy_serial.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/legacy_serial.c
> b/arch/powerpc/kernel/legacy_serial.c
> index 7b750c4..b717133 100644
> --- a/arch/powerpc/kernel/legacy_serial.c
> +++ b/arch/powerpc/kernel/legacy_serial.c
> @@ -164,6 +164,8 @@ static int __init add_legacy_soc_port(struct device_node
> *np,
>  	u64 addr;
>  	const __be32 *addrp;
>  	struct device_node *tsi = of_get_parent(np);
> +	int index = -1, len;
> +	u32 *indexp;
>  
>  	/* We only support ports that have a clock frequency properly
>  	 * encoded in the device-tree.
> @@ -188,14 +190,19 @@ static int __init add_legacy_soc_port(struct
> device_node *np,
>  	if (addr == OF_BAD_ADDR)
>  		return -1;
>  
> +	/* Check if the ports have an ordering, defined by 'cell-index' */
> +	if (((indexp = (u32*)of_get_property(np, "cell-index", &len)) !=
> NULL) &&
> +	    (len == sizeof(u32)))
> +		index = *indexp;

const u32 *

Or better, use of_read_number() or similar.

-Scott