Re: [PATCH 2/3] thunderbolt: Reset the host interface before reusing a DMA HopID

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Mon, Oct 05, 2026 at 07:13:40PM +0530, Basavaraj Natikar wrote:
> Reusing a DMA HopID without an intervening host interface reset can hang
> the TX ring on some host routers. Resetting on every DMA tunnel teardown
> clears the state but, as the reset affects all rings, also disturbs
> unrelated active tunnels.
> 
> Hence, track the DMA HopIDs programmed since the last reset, prefer unused
> HopIDs when allocating rings, and check for reuse at tb_ring_start() too,
> since networking retains its rings across reconnect. Return -EAGAIN instead
> of programming a HopID that still needs a reset.
> 
> Run the reset from a work item once all DMA rings are idle: serialize it
> with the connection manager, stop the control channel around it, and block
> DMA rings from starting during the reset. Fence the work across domain
> removal and PM transitions, preserve live DMA rings across freeze/thaw, and
> restore the interrupt-mask shadow under the NHI lock after the reset.
> 
> On -EAGAIN, retry the networking login asynchronously and block the work
> producers before teardown cancels the workers. Keep peer disconnection
> separate from administrative shutdown so it cannot reopen the login gate,
> while stream and DMA-test callers unwind immediately and return the error
> to userspace.
> 
> Enable this only for reset-capable host interfaces marked with
> QUIRK_RESET_DMA_ON_REUSE. A competing DMA tunnel must stop before its dirty
> HopID can be reused, and retrying does not interrupt that tunnel.
> 
> Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Yeah, I'm not really sure I suggested this :(

My idea was to done it so that it is nicely contained inside nhi.c without
distracting the service drivers. What you are doing is complete opposite of
that.

Given the complexity I would then rather just take the previous quirk with
the deadlock fixed.