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

["zhangjianrong (E)" <zhangjianrong5@huawei.com>]

On 6/27/2025 12:46 PM, Mika Westerberg wrote:
> Hi,
> 
> On Thu, Jun 26, 2025 at 11:50:00AM +0000, Charalampos Mitrodimas wrote:
>> Mika Westerberg <mika.westerberg@linux.intel.com> writes:
>>
>>> 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?
>>
>> I suppose this can happen when reducing bandwidth while total upstream
>> bandwidth usage on the link exceeds TB_ASYM_MIN (36 Gbps). The
>> allocation fails at the asymmetric limit check before checking whether
>> the downstream request actually needs asymmetric mode.
> 
> Right, but I would like to see here in the changelog explanation of the
> situation and preferably parts of the dmesg showing the error as well.

OK, I will update the commit message, but I don't have the dmesg because 
I can't find a host router that contains two dp adapters.

> 
> @zhangjianrong, can you do that and resend?
> 
> Note, I will be on vacation after today so expect delay from my side.
> 
>>>>
>>>> Signed-off-by: zhangjianrong <zhangjianrong5@huawei.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
>