Date:   Thu, 14 Dec 2023 12:08:34 +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 12/13/2023 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.
>>>> 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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