Subject: Re: [PATCH 04/11] of: address: Preserve the flags portion on 1:1 dma-ranges mapping

From: Rob Herring <[email-masked]>
Date: Tue, 20 Aug 2024 19:16:18 -0500

On Tue, Aug 20, 2024 at 04:36:06PM +0200, Andrea della Porta wrote:
> A missing or empty dma-ranges in a DT node implies a 1:1 mapping for dma
> translations. In this specific case, rhe current behaviour is to zero out

typo

> the entire specifier so that the translation could be carried on as an
> offset from zero.  This includes address specifier that has flags (e.g.
> PCI ranges).
> Once the flags portion has been zeroed, the translation chain is broken
> since the mapping functions will check the upcoming address specifier

What does "upcoming address" mean?

> against mismatching flags, always failing the 1:1 mapping and its entire
> purpose of always succeeding.
> Set to zero only the address portion while passing the flags through.

Can you point me to what the failing DT looks like. I'm puzzled how 
things would have worked for anyone.

> 
> Signed-off-by: Andrea della Porta <[email-masked]>
> ---
>  drivers/of/address.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index d669ce25b5f9..5a6d55a67aa8 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -443,7 +443,8 @@ static int of_translate_one(struct device_node *parent, struct of_bus *bus,
>  	}
>  	if (ranges == NULL || rlen == 0) {
>  		offset = of_read_number(addr, na);
> -		memset(addr, 0, pna * 4);
> +		/* copy the address while preserving the flags */
> +		memset(addr + pbus->flag_cells, 0, (pna - pbus->flag_cells) * 4);
>  		pr_debug("empty ranges; 1:1 translation\n");
>  		goto finish;
>  	}
> -- 
> 2.35.3
>