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

Chris Lew
2024-11-22T00:29:19Z

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.

> Johan