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

Alex Elder
2022-02-17T14:50:11Z

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