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

Manivannan Sadhasivam
2022-02-17T10:20:46Z

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