Re: [PATCH] usb: gadget: tegra-xudc: drain EP pipeline before DMA unmap

[Jon Hunter <jonathanh@nvidia.com>]

On 25/06/2026 15:53, Greg KH wrote:
> On Fri, Jun 05, 2026 at 02:16:47PM +0900, Vi_ _Ku wrote:
>> On Tegra186/194/234 the XUDC appears to post a transfer-completion
>> event when the DMA write is dispatched to the AXI interconnect, before
>> the store is committed to memory.  Under SMMU strict mode dma_unmap()
>> synchronously removes the IOVA TLB entry.  If an in-flight AXI write
>> to that IOVA has not yet been committed, the SMMU raises a translation
>> fault (fsr=0x402) that permanently wedges the bulk endpoint; the host
>> cdc_ncm TX queue stalls and fires NETDEV WATCHDOG after 5 s.
>>
>> Fix for non-control endpoints: poll EP_THREAD_ACTIVE until the endpoint
>> sequencer goes idle before calling dma_unmap().  Follow the poll with an
>> MMIO read-back that orders prior CPU writes to device memory.  Only
>> after that does dma_unmap() invalidate the TLB entry.
>>
>> On timeout, skip the dma_unmap to avoid triggering the SMMU fault.  The
>> DMA mapping leaks, but the hardware is already in an unrecoverable state
>> at that point.
>>
>> ep_wait_for_inactive() uses readl_poll_timeout_atomic() (1 µs poll,
>> 100 µs timeout), already called from IRQ context in
>> __tegra_xudc_ep_dequeue().  Change its return type from void to int so
>> both call sites can detect and report a timeout.
>>
>> Control endpoints (EP0) are excluded: their completions go through the
>> control-transfer state machine where the DMA is fully committed before
>> req_done is called.
>>
>> Fixes: d720f0f7bfa0 ("usb: gadget: Add Tegra XUSB device mode controller
>> driver")
>> Cc: stable@vger.kernel.org
>> Cc: Thierry Reding <thierry.reding@gmail.com>
>> Cc: Jonathan Hunter <jonathanh@nvidia.com>
>> Cc: Dmitry Osipenko <digetx@gmail.com>
>> Cc: linux-tegra@vger.kernel.org
>> Signed-off-by: Vishal Kumar <vishalmimani008@gmail.com>
> 
> Does not match your "From:" line :(

Looks like this patch was sent 4 times. I also had some comments here FYI ...

https://lore.kernel.org/linux-tegra/169ef7cc-e1fe-46d6-95ca-0f3514e806c0@nvidia.com/

Jon

-- 
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