Re: [PATCH 1/2] bus: mhi: core: Fix MHI runtime_pm behavior

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Mar 31, 2021 at 07:38:55PM +0200, Loic Poulain wrote:
> Hi Mani,
> 
> Le mer. 31 mars 2021 à 19:12, Manivannan Sadhasivam <
> manivannan.sadhasivam@linaro.org> a écrit :
> 
> > On Fri, Mar 05, 2021 at 06:02:23PM +0100, Loic Poulain wrote:
> > > This change ensures that PM reference is always get during packet
> > > queueing and released either after queuing completion (RX) or once
> > > the buffer has been consumed (TX). This guarantees proper update for
> > > underlying MHI controller runtime status (e.g. last_busy timestamp)
> > > and prevents suspend to be triggered while TX packets are flying,
> > > or before we completed update of the RX ring.
> > >
> >
> > Any reason why you didn't wait for RX completion also?
> 
> 
> Because on TX we know the buffer completion is going to happen really
> quickly (we send data) whereas we never know when when RX packet will be
> completed (we are waiting for data), so we want to be able to put the MHI
> device in suspend while RX is pending (the device will wake up the host on
> incoming data)
> 

Device wakeup will only happen for device initiated suspend (M1) but for
host initiated suspend (M3), device will check for pending data to host
and will initiate wakeup request before going for suspend. So I think it
is safe to wait for RX data.

Hemant/Bhaumik, any thoughts?

Thanks,
Mani

> 
> >
> > Thanks,
> > Mani
> >
> > > Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
> > > ---
> > >  drivers/bus/mhi/core/main.c | 20 ++++++++++++++++----
> > >  1 file changed, 16 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> > > index c780234..16b9640 100644
> > > --- a/drivers/bus/mhi/core/main.c
> > > +++ b/drivers/bus/mhi/core/main.c
> > > @@ -584,8 +584,11 @@ static int parse_xfer_event(struct mhi_controller
> > *mhi_cntrl,
> > >                       /* notify client */
> > >                       mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
> > >
> > > -                     if (mhi_chan->dir == DMA_TO_DEVICE)
> > > +                     if (mhi_chan->dir == DMA_TO_DEVICE) {
> > >                               atomic_dec(&mhi_cntrl->pending_pkts);
> > > +                             /* Release the reference got from
> > mhi_queue() */
> > > +                             mhi_cntrl->runtime_put(mhi_cntrl);
> > > +                     }
> > >
> > >                       /*
> > >                        * Recycle the buffer if buffer is pre-allocated,
> > > @@ -1021,9 +1024,11 @@ static int mhi_queue(struct mhi_device *mhi_dev,
> > struct mhi_buf_info *buf_info,
> > >       if (unlikely(ret))
> > >               goto exit_unlock;
> > >
> > > -     /* trigger M3 exit if necessary */
> > > -     if (MHI_PM_IN_SUSPEND_STATE(mhi_cntrl->pm_state))
> > > -             mhi_trigger_resume(mhi_cntrl);
> > > +     /* Packet is queued, take a usage ref to exit M3 if necessary
> > > +      * for host->device buffer, balanced put is done on buffer
> > completion
> > > +      * for device->host buffer, balanced put is after ringing the DB
> > > +      */
> > > +     mhi_cntrl->runtime_get(mhi_cntrl);
> > >
> > >       /* Assert dev_wake (to exit/prevent M1/M2)*/
> > >       mhi_cntrl->wake_toggle(mhi_cntrl);
> > > @@ -1034,6 +1039,9 @@ static int mhi_queue(struct mhi_device *mhi_dev,
> > struct mhi_buf_info *buf_info,
> > >       if (likely(MHI_DB_ACCESS_VALID(mhi_cntrl)))
> > >               mhi_ring_chan_db(mhi_cntrl, mhi_chan);
> > >
> > > +     if (dir == DMA_FROM_DEVICE)
> > > +             mhi_cntrl->runtime_put(mhi_cntrl);
> > > +
> > >  exit_unlock:
> > >       read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
> > >
> > > @@ -1431,6 +1439,10 @@ static void mhi_reset_data_chan(struct
> > mhi_controller *mhi_cntrl,
> > >                       result.buf_addr = buf_info->cb_buf;
> > >                       mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
> > >               }
> > > +
> > > +             /* Release the reference got from mhi_queue() */
> > > +             if (mhi_chan->dir == DMA_TO_DEVICE)
> > > +                     mhi_cntrl->runtime_put(mhi_cntrl);
> > >       }
> > >  }
> > >
> > > --
> > > 2.7.4
> > >
> >