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Date: Wed, 31 Jan 2024 18:11:36 -0800
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Subject: Re: [PATCH v12 04/41] usb: host: xhci-mem: Cleanup pending secondary
 event ring events
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To: Mathias Nyman <mathias.nyman@linux.intel.com>,
        <srinivas.kandagatla@linaro.org>, <mathias.nyman@intel.com>,
        <perex@perex.cz>, <conor+dt@kernel.org>, <corbet@lwn.net>,
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        "Neronin, Niklas" <niklas.neronin@intel.com>
References: <20240102214549.22498-1-quic_wcheng@quicinc.com>
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 <734591a1-50b4-6dc7-0b93-077355ec12e4@linux.intel.com>
 <7b2ec96b-b72f-c848-7c35-36e61a4072ac@quicinc.com>
 <b254f73b-a1bc-3dd4-f485-a3acf556835d@quicinc.com>
 <2178e799-2068-7443-59b2-310dfdd1ddee@linux.intel.com>
 <ae64ce69-dc1b-1534-7950-0a35c4a56f58@quicinc.com>
 <ff0bff8b-f26a-87bd-9762-9f2af98abcca@quicinc.com>
 <44a3d4db-7759-dd93-782a-1efbebfdb22c@linux.intel.com>
From: Wesley Cheng <quic_wcheng@quicinc.com>
In-Reply-To: <44a3d4db-7759-dd93-782a-1efbebfdb22c@linux.intel.com>
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Hi Mathias,

On 1/29/2024 7:44 AM, Mathias Nyman wrote:
> On 26.1.2024 23.13, Wesley Cheng wrote:
>> Hi Mathias,
>>
>> On 1/16/2024 12:24 PM, Wesley Cheng wrote:
>>> Hi Mathias,
>>>
>>> On 1/15/2024 6:01 AM, Mathias Nyman wrote:
>>>> On 10.1.2024 1.42, Wesley Cheng wrote:
>>>>> Hi Mathias,
>>>>>
>>>>> On 1/8/2024 12:51 PM, Wesley Cheng wrote:
>>>>>> Hi Mathias,
>>>>>>
>>>>>> On 1/4/2024 6:48 AM, Mathias Nyman wrote:
>>>>>>> On 2.1.2024 23.45, Wesley Cheng wrote:
>>>>>>>> As part of xHCI bus suspend, the XHCI is halted.  However, if 
>>>>>>>> there are
>>>>>>>> pending events in the secondary event ring, it is observed that 
>>>>>>>> the xHCI
>>>>>>>> controller stops responding to further commands upon host or device
>>>>>>>> initiated bus resume.  Iterate through all pending events and 
>>>>>>>> update the
>>>>>>>> dequeue pointer to the beginning of the event ring.
>>>>>>>>
>>>>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>>>>>>> ...
>>>>>>>> +/*
>>>>>>>> + * Move the event ring dequeue pointer to skip events kept in 
>>>>>>>> the secondary
>>>>>>>> + * event ring.  This is used to ensure that pending events in 
>>>>>>>> the ring are
>>>>>>>> + * acknowledged, so the XHCI HCD can properly enter 
>>>>>>>> suspend/resume. The
>>>>>>>> + * secondary ring is typically maintained by an external 
>>>>>>>> component.
>>>>>>>> + */
>>>>>>>> +void xhci_skip_sec_intr_events(struct xhci_hcd *xhci,
>>>>>>>> +    struct xhci_ring *ring,    struct xhci_interrupter *ir)
>>>>>>>> +{
>>>>>>>> +    union xhci_trb *erdp_trb, *current_trb;
>>>>>>>> +    u64 erdp_reg;
>>>>>>>> +    u32 iman_reg;
>>>>>>>> +    dma_addr_t deq;
>>>>>>>> +
>>>>>>>> +    /* disable irq, ack pending interrupt and ack all pending 
>>>>>>>> events */
>>>>>>>> +    xhci_disable_interrupter(ir);
>>>>>>>> +    iman_reg = readl_relaxed(&ir->ir_set->irq_pending);
>>>>>>>> +    if (iman_reg & IMAN_IP)
>>>>>>>> +        writel_relaxed(iman_reg, &ir->ir_set->irq_pending);
>>>>>>>> +
>>>>>>>> +    /* last acked event trb is in erdp reg  */
>>>>>>>> +    erdp_reg = xhci_read_64(xhci, &ir->ir_set->erst_dequeue);
>>>>>>>> +    deq = (dma_addr_t)(erdp_reg & ERST_PTR_MASK);
>>>>>>>> +    if (!deq) {
>>>>>>>> +        xhci_err(xhci, "event ring handling not required\n");
>>>>>>>> +        return;
>>>>>>>> +    }
>>>>>>>> +
>>>>>>>> +    erdp_trb = current_trb = ir->event_ring->dequeue;
>>>>>>>> +    /* read cycle state of the last acked trb to find out CCS */
>>>>>>>> +    ring->cycle_state = 
>>>>>>>> le32_to_cpu(current_trb->event_cmd.flags) & TRB_CYCLE;
>>>>>>>> +
>>>>>>>> +    while (1) {
>>>>>>>> +        inc_deq(xhci, ir->event_ring);
>>>>>>>> +        erdp_trb = ir->event_ring->dequeue;
>>>>>>>> +        /* cycle state transition */
>>>>>>>> +        if ((le32_to_cpu(erdp_trb->event_cmd.flags) & 
>>>>>>>> TRB_CYCLE) !=
>>>>>>>> +            ring->cycle_state)
>>>>>>>> +            break;
>>>>>>>> +    }
>>>>>>>> +
>>>>>>>> +    xhci_update_erst_dequeue(xhci, ir, current_trb, true);
>>>>>>>> +}
>>>>>>>
>>>>>>> Code above is very similar to the existing event ring processing 
>>>>>>> parts of xhci_irq()
>>>>>>> and xhci_handle_event()
>>>>>>>
>>>>>>> I'll see if I can refactor the existing event ring processing, 
>>>>>>> decouple it from
>>>>>>> event handling so that it could be used by primary and secondary 
>>>>>>> interrupters with
>>>>>>> handlers, and this case where we just want to clear the event ring.
>>>>>>>
>>>>>>
>>>>>> Thanks, that makes sense.  Will take a look as well.
>>>>>>
>>>>>
>>>>> How about something like the below?  Tested this on my set up and 
>>>>> everything looks to be working fine.  Had to add another param to 
>>>>> struct xhci_interrupters to tell the XHCI interrupt handler to say 
>>>>> if that particular interrupter wants to skip_events (handling).  
>>>>> This way, its something that the class driver utilizing the 
>>>>> interrupter will have to tell XHCI sideband.  It would allow the 
>>>>> user to determine if they want to use the interrupter to actually 
>>>>> handle events or not on the proc running Linux.
>>>>>
>>>>
>>>> Yes, I have something similar.
>>>> I'll share it soon, just need to
>>>> clean it up a bit fist.
>>>>
>>>
>>> Sure, no worries.  Will test it when its available.  Thanks!
>>>
>>
>> Was just wondering if you had the time to clean up the changes?  If 
>> not, maybe you can provide a patch with whatever you have, and I can 
>> try my best to clean it up to your liking?  Thanks!
> 
> Sure, got stuck fixing other issues.
>

No worries, tested the code briefly as is and it is working, with some 
minor modifications.

> Code is not yet cleaned up, commit messages are not ready etc, but 
> current work is in
> a fix_eventhandling branch:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git  
> fix_eventhandling
> https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=fix_eventhandling 
> 
> 
> I was in the middle of figuring out when and where the ip_autoclear and 
> interrupt
> moderation values should be set for secondary interrupters
> 

I set these currently when the client driver requests for the 
interrupter, ie xhci_sideband_create_interrupter().  If the client 
driver wants to actually have the secondary interrupter events handled 
by the OS then I added a path to call xhci_enable_interrupter() to 
enable that IRQ line.  Likewise, based on XHCI spec Figure 4-22, the 
IMAN interrupt enable (IE) bit controls basically when IMOD and IP 
autoclear mechanisms would come into the picture, so I placed these 
configurations before we set the IE bit.

For the most part, if we offload event ring handling to another 
processor, then IMOD and IE settings would be irrelevant IMO.

The only pitfall with this is that it gets a bit cumbersome (although 
flexible) for the client driver to know what these arguments actually do 
within the XHCI layer.  Working through your changes and will push 
something soon.  Thanks again for sharing the changes!

Thanks
Wesley Cheng