Date:   Thu, 14 Dec 2023 12:50:21 +0530
From:   Sanath S <sanaths2@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Sanath S <Sanath.S@....com>, mario.limonciello@....com,
        andreas.noever@...il.com, michael.jamet@...el.com,
        YehezkelShB@...il.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v2 2/2] thunderbolt: Teardown tunnels and reset downstream
 ports created by boot firmware


On 12/14/2023 12:37 PM, Mika Westerberg wrote:
> On Thu, Dec 14, 2023 at 12:08:34PM +0530, Sanath S wrote:
>> On 12/13/2023 5:22 PM, Mika Westerberg wrote:
>>> On Wed, Dec 13, 2023 at 04:04:57PM +0530, Sanath S wrote:
>>>> On 12/13/2023 11:53 AM, Mika Westerberg wrote:
>>>>> On Wed, Dec 13, 2023 at 08:18:06AM +0200, Mika Westerberg wrote:
>>>>>> On Wed, Dec 13, 2023 at 07:49:14AM +0200, Mika Westerberg wrote:
>>>>>>> On Wed, Dec 13, 2023 at 12:46:35AM +0530, Sanath S wrote:
>>>>>>>> Boot firmware might have created tunnels of its own. Since we cannot
>>>>>>>> be sure they are usable for us. Tear them down and reset the ports
>>>>>>>> to handle it as a new hotplug for USB3 routers.
>>>>>>>>
>>>>>>>> Suggested-by: Mario Limonciello <mario.limonciello@....com>
>>>>>>>> Signed-off-by: Sanath S <Sanath.S@....com>
>>>>>>>> ---
>>>>>>>>     drivers/thunderbolt/tb.c | 11 +++++++++++
>>>>>>>>     1 file changed, 11 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
>>>>>>>> index fd49f86e0353..febd0b6972e3 100644
>>>>>>>> --- a/drivers/thunderbolt/tb.c
>>>>>>>> +++ b/drivers/thunderbolt/tb.c
>>>>>>>> @@ -2598,6 +2598,17 @@ static int tb_start(struct tb *tb)
>>>>>>>>     	tb_switch_tmu_enable(tb->root_switch);
>>>>>>>>     	/* Full scan to discover devices added before the driver was loaded. */
>>>>>>>>     	tb_scan_switch(tb->root_switch);
>>>>>>>> +	/*
>>>>>>>> +	 * Boot firmware might have created tunnels of its own. Since we cannot
>>>>>>>> +	 * be sure they are usable for us, Tear them down and reset the ports
>>>>>>>> +	 * to handle it as new hotplug for USB4 routers.
>>>>>>>> +	 */
>>>>>>>> +	if (tb_switch_is_usb4(tb->root_switch)) {
>>>>>>>> +		tb_switch_discover_tunnels(tb->root_switch,
>>>>>>>> +					   &tcm->tunnel_list, false);
>>>>>>> Why this is needed?
>>>>>>>
>>>>>>> It should be enough, to do simply something like this:
>>>>>>>
>>>>>>> 	if (tb_switch_is_usb4(tb->root_switch))
>>>>>>> 		tb_switch_reset(tb->root_switch);
>>>> If we don't tear down of tunnels before performing the DPR, the PCIe
>>>> enumeration is failing.
>>>>
>>>> PCIe link is not coming up after DPR. Below log is missing without
>>>> performing path
>>>> deactivation before performing DPR and hence PCIe enumeration is not
>>>> initiated.
>>>>
>>>> [  746.630865] pcieport 0000:00:03.1: pciehp: Slot(0-1): Card present
>>>> [  746.630885] pcieport 0000:00:03.1: pciehp: Slot(0-1): Link Up
>>>>
>>>> I think when we do a DPR, it internally does some handling with PCI Path
>>>> Enable bit(PE).
>>>> So, deactivation of PCIe path is necessary for DPR to work.
>>> Rigth, it should be enough to reset the protocol adapter config and path
>>> config spaces. I guess using discovery at this point is fine too but I
>>> would at least check how complex doing the minimal "reset" turns out.
>>>
>>> I mean in tb_switch_reset() for USB4 v1 routers it can go over all the
>>> adapters and perform "cleanup" or so.
>> I gave it a thought yesterday and we can do something like this:
>>
>> We are already doing tb_discovery(tb) in tb_start. This would
>> discover the path configuration done by Boot firmware.
>>
>> Now, we can place the tb_switch_reset() right below that api with
>> conditions suggested by you.
>>
>> And tb_switch_reset() would internally DPR for all down steam ports.
>>
>> It can look something like below:
>>
>>      /* Find out tunnels created by the boot firmware */
>>          tb_discover_tunnels(tb);
>>      /*
>>       * Reset USB4 v1 host router to get rid of possible tunnels the
>>       * boot firmware created. This makes sure all the tunnels are
>>       * created by us and thus have known configuration.
>>       *
>>       * For USB4 v2 and beyond we do this in nhi_reset() using the
>>       * host router reset interface.
>>       */
>>      if (host_reset && usb4_switch_version(tb->root_switch) == 1)
>>          tb_switch_reset(tb->root_switch);
>>
>> With this, we are making sure while we get a unplug event after doing a DPR,
>> We are clearing all the paths established by Boot firmware. This wouldn't be
>> possible
>> if we had not discovered the paths before we perform DPR.
>>
>> It would create inconsistency for a new hot plug if we have not cleared the
>> path configurations
>> of previous hot unplug events.
> Right. I would still check if doing protocol adapter "reset" + path
> config space clear in tb_switch_reset() is enough and how complex that
> ends up to be. I think that's all what is needed.
>
> If it turns out too complex, yes I guess something like this:
>
> 	/* Find out tunnels created by the boot firmware */
> 	tb_discover_tunnels(tb);
> 	/* Add DP resources from the DP tunnels created by the boot firmware */
> 	tb_discover_dp_resources(tb);
>
> 	if (host_reset && usb4_switch_version(tb->root_switch) == 1) {
> 		struct tb_tunnel *n, *tunnel;
>
> 		list_for_each_entry_safe(tunnel, n, &tcm->tunnel_list, list)
> 			tb_deactivate_and_free_tunnel(tunnel);
>
> 		tb_switch_reset(tb->root_switch);
> 	}
>
> With proper comments would work, no?
Yes, this works. Tested it too and works fine.
Probably we can move tb_deactivate_and_free_tunnel() inside 
tb_switch_reset() to make it
look better.
> Regarding "host_reset", I think we can actually keep it in nhi.c and add
> a parameter to cm_ops->start(reset) that gets passed to the "CM
> implementation". Or something along those lines.
I will check along these lines.
>>>>>> Actually this needs to be done only for USB4 v1 routers since we already
>>>>>> reset USB4 v2 hosts so something like:
>>>>>>
>>>>>> 	/*
>>>>>> 	 * Reset USB4 v1 host router to get rid of possible tunnels the
>>>>>> 	 * boot firmware created. This makes sure all the tunnels are
>>>>>> 	 * created by us and thus have known configuration.
>>>>>> 	 *
>>>>>> 	 * For USB4 v2 and beyond we do this in nhi_reset() using the
>>>>>> 	 * host router reset interface.
>>>>>> 	 */
>>>>>> 	if (usb4_switch_version(tb->root_switch) == 1)
>>>>>> 		tb_switch_reset(tb->root_switch);
>>>>>>
>>>>>> (possibly add similar comment to the nhi_reset() to refer this one).
>>>>> Oh, and would it be possible to tie this with the "host_reset" parameter
>>>>> too somehow? I guess it could be moved to "tb.c" and "tb.h" and then
>>>>> check it from nhi.c as already done and then here so this would become:
>>>>>
>>>>>     	if (host_reset && usb4_switch_version(tb->root_switch) == 1)
>>>>>     		tb_switch_reset(tb->root_switch);
>>>> Is host_reset necessary for USB4 v1 routers ? I did not use host_reset in
>>>> this case.
>>>> If its needed, then we have to modify to enable host_reset in nhi.c as well.
>>> Well you are effectively doing that here, no? You "reset" the host
>>> router therefore tying this to the same command line parameter makes
>>> sense and allows user an "escape hatch" if this turns out breaking
>>> things.

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