Re: [PATCH v2 3/6] bus: mhi: core: Add support to stop or start channel data transfers

[Bhaumik Bhatt]

Hi Mani,

On 2020-11-16 04:43, Manivannan Sadhasivam wrote:
> On Wed, Nov 11, 2020 at 11:21:10AM -0800, Bhaumik Bhatt wrote:
> > Some MHI client drivers may want to request a pause or halt of
> > data transfer activity on their channels. Support for this does
> > not exist and must be introduced, wherein the channel context is
> > not reset or cleared but only the STOP channel command is issued.
> > This would need to be paired with an API that allows resuming the
> > data transfer activity on channels by use of the START channel
> > command. This API assumes that the context information is already
> > setup. Enable this using two new APIs, mhi_start_transfer() and
> > mhi_stop_transfer().
> >
> > Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> > ---
> >  drivers/bus/mhi/core/main.c | 41 
> > +++++++++++++++++++++++++++++++++++++++++
> >  include/linux/mhi.h         | 19 +++++++++++++++++++
> >  2 files changed, 60 insertions(+)
> >
> > diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> > index 1226933..1a969f4 100644
> > --- a/drivers/bus/mhi/core/main.c
> > +++ b/drivers/bus/mhi/core/main.c
> > @@ -1560,6 +1560,47 @@ void mhi_unprepare_from_transfer(struct 
> > mhi_device *mhi_dev)
> >  }
> >  EXPORT_SYMBOL_GPL(mhi_unprepare_from_transfer);
> >
> > +static int mhi_update_transfer_state(struct mhi_device *mhi_dev,
> > +				     enum mhi_ch_state_type to_state)
> > +{
> > +	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
> > +	struct mhi_chan *mhi_chan;
> > +	int dir, ret;
> > +
> > +	for (dir = 0; dir < 2; dir++) {
> > +		mhi_chan = dir ? mhi_dev->ul_chan : mhi_dev->dl_chan;
> > +
> > +		if (!mhi_chan)
> > +			continue;
> > +
> > +		/*
> > +		 * Bail out if one of the channels fail as client will reset
> > +		 * both upon failure
> > +		 */
> > +		mutex_lock(&mhi_chan->mutex);
>
> Hmm. The documentation about wait_for_completion*() used in
> mhi_update_channel_state()says below,
>
> "As all variants of wait_for_completion() can (obviously) block for a 
> long
> time depending on the nature of the activity they are waiting for, so 
> in
> most cases you probably don't want to call this with held mutexes."
Yes, that is understood. The mhi_chan->mutex is only used to lock any 
channel
enable/start/stop/disable type operations, since these have to be in 
order, it
is essential that we wait for one of the operations to finish before the 
next
one.

Also we avoid a race, for example, at a time when a device crash forces 
a driver
"remove" call, while an operation to start/stop a channel is already 
going on.
> > +		ret = mhi_update_channel_state(mhi_cntrl, mhi_chan, to_state);
> > +		if (ret) {
> > +			mutex_unlock(&mhi_chan->mutex);
> > +			return ret;
> > +		}
> > +		mutex_unlock(&mhi_chan->mutex);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +int mhi_stop_transfer(struct mhi_device *mhi_dev)
> > +{
> > +	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_STOP);
> > +}
> > +EXPORT_SYMBOL_GPL(mhi_stop_transfer);
> > +
> > +int mhi_start_transfer(struct mhi_device *mhi_dev)
> > +{
> > +	return mhi_update_transfer_state(mhi_dev, MHI_CH_STATE_TYPE_START);
> > +}
> > +EXPORT_SYMBOL_GPL(mhi_start_transfer);
> > +
> >  int mhi_poll(struct mhi_device *mhi_dev, u32 budget)
> >  {
> >  	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
> > diff --git a/include/linux/mhi.h b/include/linux/mhi.h
> > index 52b3c60..aee8494 100644
> > --- a/include/linux/mhi.h
> > +++ b/include/linux/mhi.h
> > @@ -702,6 +702,25 @@ int mhi_prepare_for_transfer(struct mhi_device 
> > *mhi_dev);
> >  void mhi_unprepare_from_transfer(struct mhi_device *mhi_dev);
> >
> >  /**
> > + * mhi_stop_transfer - Pauses ongoing channel activity by issuing the 
> > STOP
> > + *                     channel command to both UL and DL channels. 
> > This command
> > + *                     does not reset the channel context and the 
> > client drivers
> > + *                     can issue mhi_start_transfer to resume 
> > activity.
> > + * @mhi_dev: Device associated with the channels
> > + */
> > +int mhi_stop_transfer(struct mhi_device *mhi_dev);
> > +
> > +/**
> > + * mhi_start_transfer - Resumes channel activity by issuing the START 
> > channel
> > + *                      command to both UL and DL channels. This 
> > command assumes
> > + *                      the channel context is already setup and the 
> > client
> > + *                      drivers can issue mhi_stop_transfer to pause 
> > activity if
> > + *                      required.
> > + * @mhi_dev: Device associated with the channels
> > + */
> > +int mhi_start_transfer(struct mhi_device *mhi_dev);
> > +
> > +/**
>
> Align the comment header properly.
So I am trying to follow the documentation style for other functions in 
the same
file. Is there any particular format you want me to refer to?

I use all spaces for the lines after the first one to align them just 
like the
rest of them.

> Thanks,
> Mani
>
> >   * mhi_poll - Poll for any available data in DL direction
> >   * @mhi_dev: Device associated with the channels
> >   * @budget: # of events to process
> > --
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
> > Forum,
> > a Linux Foundation Collaborative Project

Thanks,
Bhaumik
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum,
a Linux Foundation Collaborative Project