Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation

[Chris Lew <quic_clew@quicinc.com>]

On 11/24/2024 7:04 AM, Manivannan Sadhasivam wrote:
> On Thu, Nov 21, 2024 at 04:28:41PM -0800, Chris Lew wrote:
>>
>>
>> On 11/8/2024 2:32 AM, Johan Hovold wrote:
>>> On Mon, Nov 04, 2024 at 05:29:37PM -0800, Chris Lew wrote:
>>>> From: Bhaumik Bhatt <bbhatt@codeaurora.org>
>>>>
>>>> The call to qrtr_endpoint_register() was moved before
>>>> mhi_prepare_for_transfer_autoqueue() to prevent a case where a dl
>>>> callback can occur before the qrtr endpoint is registered.
>>>>
>>>> Now the reverse can happen where qrtr will try to send a packet
>>>> before the channels are prepared. Add a wait in the sending path to
>>>> ensure the channels are prepared before trying to do a ul transfer.
>>>>
>>>> Fixes: 68a838b84eff ("net: qrtr: start MHI channel after endpoit creation")
>>>> Reported-by: Johan Hovold <johan@kernel.org>
>>>> Closes: https://lore.kernel.org/linux-arm-msm/ZyTtVdkCCES0lkl4@hovoldconsulting.com/
>>>> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
>>>> Signed-off-by: Chris Lew <quic_clew@quicinc.com>
>>>
>>>> @@ -53,6 +54,10 @@ static int qcom_mhi_qrtr_send(struct qrtr_endpoint *ep, struct sk_buff *skb)
>>>>    	if (skb->sk)
>>>>    		sock_hold(skb->sk);
>>>> +	rc = wait_for_completion_interruptible(&qdev->prepared);
>>>> +	if (rc)
>>>> +		goto free_skb;
>>>> +
>>>>    	rc = skb_linearize(skb);
>>>>    	if (rc)
>>>>    		goto free_skb;
>>>> @@ -85,6 +90,7 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
>>>>    	qdev->mhi_dev = mhi_dev;
>>>>    	qdev->dev = &mhi_dev->dev;
>>>>    	qdev->ep.xmit = qcom_mhi_qrtr_send;
>>>> +	init_completion(&qdev->prepared);
>>>>    	dev_set_drvdata(&mhi_dev->dev, qdev);
>>>>    	rc = qrtr_endpoint_register(&qdev->ep, QRTR_EP_NID_AUTO);
>>>> @@ -97,6 +103,7 @@ static int qcom_mhi_qrtr_probe(struct mhi_device *mhi_dev,
>>>>    		qrtr_endpoint_unregister(&qdev->ep);
>>>>    		return rc;
>>>>    	}
>>>> +	complete_all(&qdev->prepared);
>>>>    	dev_dbg(qdev->dev, "Qualcomm MHI QRTR driver probed\n");
>>>
>>> While this probably works, it still looks like a bit of a hack.
>>>
>>> Why can't you restructure the code so that the channels are fully
>>> initialised before you register or enable them instead?
>>>
>>
>> Ok, I think we will have to stop using the autoqueue feature of MHI and
>> change the flow to be mhi_prepare_for_transfer() -->
>> qrtr_endpoint_register() --> mhi_queue_buf(DMA_FROM_DEVICE). This would make
>> it so ul_transfers only happen after mhi_prepare_for_transfer() and
>> dl_transfers happen after qrtr_endpoint_register().
>>
>> I'll take a stab at implementing this.
>>
> 
> Hmm, I thought 'autoqueue' was used for a specific reason. So it is not valid
> now?
> 

I think when MHI was being developed, I asked for an interface similar 
to rpmsg. The team came up with the autoqueue feature which made the 
qrtr mhi transport simpler and closer to the smd transport. I can't 
think of a specific reason that QRTR needs autoqueue, but maybe ill find 
it when I start poking at it.

> - Mani
>