linux-kernel - Re: [PATCH] thunderbolt: Confirm the necessity to configure asym link first

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Message-ID: <20250626093026.GJ2824380@black.fi.intel.com>
Date: Thu, 26 Jun 2025 12:30:26 +0300
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: zhangjianrong <zhangjianrong5@...wei.com>
Cc: andreas.noever@...il.com, michael.jamet@...el.com,
	YehezkelShB@...il.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, guhengsheng@...ilicon.com,
	caiyadong@...wei.com, xuetao09@...wei.com, lixinghang1@...wei.com
Subject: Re: [PATCH] thunderbolt: Confirm the necessity to configure asym
 link first

Hi,

On Thu, Jun 26, 2025 at 04:41:07PM +0800, zhangjianrong wrote:
> Current implementation can cause allocation failures in
> tb_alloc_dp_bandwidth() in some cases. For example:
> allocated_down(30Gbps), allocated_up(50Gbps),
> requested_down(10Gbps).

I'm not sure I understand the above.

Can you describe in which real life situation this can happen?

> 
> Signed-off-by: zhangjianrong <zhangjianrong5@...wei.com>
> ---
>  drivers/thunderbolt/tb.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> index a7c6919fbf97..558455d9716b 100644
> --- a/drivers/thunderbolt/tb.c
> +++ b/drivers/thunderbolt/tb.c
> @@ -1039,6 +1039,9 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
>  			break;
>  
>  		if (downstream) {
> +			/* Does consumed + requested exceed the threshold */
> +			if (consumed_down + requested_down < asym_threshold)
> +				continue;
>  			/*
>  			 * Downstream so make sure upstream is within the 36G
>  			 * (40G - guard band 10%), and the requested is above
> @@ -1048,20 +1051,17 @@ static int tb_configure_asym(struct tb *tb, struct tb_port *src_port,
>  				ret = -ENOBUFS;
>  				break;
>  			}
> -			/* Does consumed + requested exceed the threshold */
> -			if (consumed_down + requested_down < asym_threshold)
> -				continue;
>  
>  			width_up = TB_LINK_WIDTH_ASYM_RX;
>  			width_down = TB_LINK_WIDTH_ASYM_TX;
>  		} else {
>  			/* Upstream, the opposite of above */
> +			if (consumed_up + requested_up < asym_threshold)
> +				continue;
>  			if (consumed_down + requested_down >= TB_ASYM_MIN) {
>  				ret = -ENOBUFS;
>  				break;
>  			}
> -			if (consumed_up + requested_up < asym_threshold)
> -				continue;
>  
>  			width_up = TB_LINK_WIDTH_ASYM_TX;
>  			width_down = TB_LINK_WIDTH_ASYM_RX;
> -- 
> 2.34.1