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

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On 2021-07-22 12:50, Bhaumik Bhatt wrote:
On 2021-07-22 12:04 PM, Bhaumik Bhatt wrote:
On 2021-07-21 03:27 PM, hemantk@xxxxxxxxxxxxxx wrote:
On 2021-07-21 11:07, Bhaumik Bhatt wrote:
On 2021-07-21 10:52 AM, hemantk@xxxxxxxxxxxxxx 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@xxxxxxxxxxxxxx>
---
 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.
Thanks for checking that, Bhaumik.

Reviewed-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
---
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project



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