linux-kernel - Re: [PATCH v3 09/25] bus: mhi: ep: Add support for registering MHI endpoint client drivers

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Date:   Thu, 17 Feb 2022 15:50:38 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     mhi@...ts.linux.dev, quic_hemantk@...cinc.com,
        quic_bbhatt@...cinc.com, quic_jhugo@...cinc.com,
        vinod.koul@...aro.org, bjorn.andersson@...aro.org,
        dmitry.baryshkov@...aro.org, quic_vbadigan@...cinc.com,
        quic_cang@...cinc.com, quic_skananth@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 09/25] bus: mhi: ep: Add support for registering MHI
 endpoint client drivers

On Tue, Feb 15, 2022 at 02:02:50PM -0600, Alex Elder wrote:

[...]

> > +static int mhi_ep_driver_remove(struct device *dev)
> > +{
> > +	struct mhi_ep_device *mhi_dev = to_mhi_ep_device(dev);
> > +	struct mhi_ep_driver *mhi_drv = to_mhi_ep_driver(dev->driver);
> > +	struct mhi_result result = {};
> > +	struct mhi_ep_chan *mhi_chan;
> > +	int dir;
> > +
> > +	/* Skip if it is a controller device */
> > +	if (mhi_dev->dev_type == MHI_DEVICE_CONTROLLER)
> > +		return 0;
> > +
> 
> It would be my preference to encapsulate the body of the
> following loop into a called function, then call that once
> for the UL channel and once for the DL channel.
> 

This follows the host stack, so I'd like to keep it the same.

> > +	/* Disconnect the channels associated with the driver */
> > +	for (dir = 0; dir < 2; dir++) {
> > +		mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
> > +
> > +		if (!mhi_chan)
> > +			continue;
> > +
> > +		mutex_lock(&mhi_chan->lock);
> > +		/* Send channel disconnect status to the client driver */
> > +		if (mhi_chan->xfer_cb) {
> > +			result.transaction_status = -ENOTCONN;
> > +			result.bytes_xferd = 0;
> > +			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
> 
> It appears the result is ignored here.  If so, can we
> define the xfer_cb() function so that a NULL pointer may
> be supplied by the caller in cases like this?
> 

result is not ignored, only the bytes_xfered. "transaction_status" will
be used by the client drivers for error handling.

> > +		}
> > +
> > +		/* Set channel state to DISABLED */
> 
> That comment is a little tautological.  Just omit it.
> 
> > +		mhi_chan->state = MHI_CH_STATE_DISABLED;
> > +		mhi_chan->xfer_cb = NULL;
> > +		mutex_unlock(&mhi_chan->lock);
> > +	}
> > +
> > +	/* Remove the client driver now */
> > +	mhi_drv->remove(mhi_dev);
> > +
> > +	return 0;
> > +}

[...]

> > +struct mhi_ep_driver {
> > +	const struct mhi_device_id *id_table;
> > +	struct device_driver driver;
> > +	int (*probe)(struct mhi_ep_device *mhi_ep,
> > +		     const struct mhi_device_id *id);
> > +	void (*remove)(struct mhi_ep_device *mhi_ep);
> 
> I get confused by the "ul" versus "dl" naming scheme here.
> Is "ul" from the perspective of the host, meaning upload
> is from the host toward the WWAN network (and therefore
> toward the SDX AP), and download is from the WWAN toward
> the host?  Somewhere this should be stated clearly in
> comments; maybe I just missed it.
> 

Yes UL and DL are as per host context. I didn't state this explicitly
since this is the MHI host stack behaviour but I'll add a comment for
clarity

Thanks,
Mani