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

[Alex Elder]

On 2/17/22 4:20 AM, Manivannan Sadhasivam wrote:
> 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.

I think you should change both, but I'll leave that up to you.

> > > +	/* 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.

Sorry, I was looking at the code *after* the call, and was
ignoring that it was information being passed in...  My
mistake.

> > > +		}
> > > +
> > > +		/* 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

Sounds good, thanks.

					-Alex

> Thanks,
> Mani