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

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Message-ID: <b1e22673-2768-445c-8c67-eae93206cca5@quicinc.com>
Date: Thu, 21 Nov 2024 16:28:41 -0800
From: Chris Lew <quic_clew@...cinc.com>
To: Johan Hovold <johan@...nel.org>
CC: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "David S.
 Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        Simon Horman
	<horms@...nel.org>,
        Hemant Kumar <quic_hemantk@...cinc.com>,
        Loic Poulain
	<loic.poulain@...aro.org>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        "Manivannan
 Sadhasivam" <mani@...nel.org>,
        Bjorn Andersson
	<bjorn.andersson@....qualcomm.com>,
        <linux-arm-msm@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Bhaumik Bhatt
	<bbhatt@...eaurora.org>
Subject: Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation



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@...eaurora.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@...nel.org>
>> Closes: https://lore.kernel.org/linux-arm-msm/ZyTtVdkCCES0lkl4@hovoldconsulting.com/
>> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
>> Signed-off-by: Chris Lew <quic_clew@...cinc.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