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Date:   Wed, 21 Jul 2021 11:07:02 -0700
From:   Bhaumik Bhatt <bbhatt@codeaurora.org>
To:     hemantk@codeaurora.org
Cc:     manivannan.sadhasivam@linaro.org, bqiang@codeaurora.org,
        linux-arm-msm@vger.kernel.org, clew@codeaurora.org,
        linux-kernel@vger.kernel.org, bbhatt=codeaurora.org@codeaurora.org,
        hemantk=codeaurora.org@codeaurora.org
Subject: Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation
Organization: Qualcomm Innovation Center, Inc.
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On 2021-07-21 10:52 AM, hemantk@codeaurora.org wrote:
> On 2021-07-20 18:42, Bhaumik Bhatt wrote:
>> A dl callback can be received anytime after mhi_prepare_for_transfer
>> has been called. There is a window where the callback may happen
>> before the probe initializes the qrtr_mhi_dev state. Move the
>> mhi_prepare_for_transfer call after the registering the endpoint.
>> 
>> Once moved, 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: a2e2cc0dbb11 ("net: qrtr: Start MHI channels during init")
>> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
>> ---
>>  net/qrtr/mhi.c | 20 +++++++++++++++-----
>>  1 file changed, 15 insertions(+), 5 deletions(-)
>> 
>> diff --git a/net/qrtr/mhi.c b/net/qrtr/mhi.c
>> index 29b4fa3..22b0395 100644
>> --- a/net/qrtr/mhi.c
>> +++ b/net/qrtr/mhi.c
>> @@ -15,6 +15,7 @@ struct qrtr_mhi_dev {
>>  	struct qrtr_endpoint ep;
>>  	struct mhi_device *mhi_dev;
>>  	struct device *dev;
>> +	struct completion ready;
>>  };
>> 
>>  /* From MHI to QRTR */
>> @@ -50,6 +51,10 @@ static int qcom_mhi_qrtr_send(struct qrtr_endpoint
>> *ep, struct sk_buff *skb)
>>  	struct qrtr_mhi_dev *qdev = container_of(ep, struct qrtr_mhi_dev, 
>> ep);
>>  	int rc;
>> 
>> +	rc = wait_for_completion_interruptible(&qdev->ready);
>> +	if (rc)
>> +		goto free_skb;
>> +
>>  	if (skb->sk)
>>  		sock_hold(skb->sk);
>> 
>> @@ -78,11 +83,6 @@ static int qcom_mhi_qrtr_probe(struct mhi_device 
>> *mhi_dev,
>>  	struct qrtr_mhi_dev *qdev;
>>  	int rc;
>> 
>> -	/* start channels */
>> -	rc = mhi_prepare_for_transfer(mhi_dev, MHI_CH_INBOUND_ALLOC_BUFS);
>> -	if (rc)
>> -		return rc;
>> -
>>  	qdev = devm_kzalloc(&mhi_dev->dev, sizeof(*qdev), GFP_KERNEL);
>>  	if (!qdev)
>>  		return -ENOMEM;
> would it be good to init completion variable here (call 
> init_completion) ?
You mean just before setting qdev->mhi_dev? I don't see why that would 
make a difference
mainly because the qcom_mhi_qrtr_send() will only happen after endpoint 
is
registered and DL xfer cb will also only come in after we have prepared 
the
channels and completed ready with dev_data already set.

>> @@ -90,12 +90,22 @@ 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->ready);
>> 
> 
>> 
>>  	return 0;

Thanks,
Bhaumik
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