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Date:   Wed, 21 Jul 2021 10:52:30 -0700
From:   hemantk@...eaurora.org
To:     Bhaumik Bhatt <bbhatt@...eaurora.org>
Cc:     manivannan.sadhasivam@...aro.org, bqiang@...eaurora.org,
        linux-arm-msm@...r.kernel.org, clew@...eaurora.org,
        linux-kernel@...r.kernel.org, bbhatt=codeaurora.org@...eaurora.org
Subject: Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation

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@...eaurora.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) 
?
> @@ -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;

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