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Date:   Thu, 22 Jul 2021 12:50:32 -0700
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     hemantk@...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,
        hemantk=codeaurora.org@...eaurora.org
Subject: Re: [PATCH] net: qrtr: mhi: synchronize qrtr and mhi preparation

On 2021-07-22 12:04 PM, Bhaumik Bhatt wrote:
> On 2021-07-21 03:27 PM, hemantk@...eaurora.org wrote:
>> On 2021-07-21 11:07, Bhaumik Bhatt wrote:
>>> On 2021-07-21 10:52 AM, hemantk@...eaurora.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@...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) ?
>>> 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.
>> looks like qcom_mhi_qrtr_send is not going to get called directly. i
>> was thinking
>> what if this api is called before init_completion() returns. if it is
>> only possible
>> through ep.xmit call back only, can you move it right above
>> qdev->ep.xmit = qcom_mhi_qrtr_send; ?
>>> 
> Ah. OK. I see your point. I will do that and upload a v2.
> 
On second thought, this is not required because the ep.xmit() will not 
be called
until the qrtr_endpoint_register() is done.

So this version should be fine IMO.

>>>>> @@ -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
>>> ---
>>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>>> Forum,
>>> a Linux Foundation Collaborative Project
>> 
>> Thanks,
>> Hemant
>> ---
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
> 
> Thanks,
> Bhaumik
> ---
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
> Forum,
> a Linux Foundation Collaborative Project

Thanks,
Bhaumik
---
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
a Linux Foundation Collaborative Project

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