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

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Message-ID: <20241124150422.nt67aonfknfhz3sc@thinkpad>
Date: Sun, 24 Nov 2024 20:34:22 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Chris Lew <quic_clew@...cinc.com>
Cc: Johan Hovold <johan@...nel.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 Thu, Nov 21, 2024 at 04:28:41PM -0800, Chris Lew wrote:
> 
> 
> 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.
> 

Hmm, I thought 'autoqueue' was used for a specific reason. So it is not valid
now?

- Mani

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