linux-kernel - Re: [PATCH 6/8] bus: mhi: core: Add support for processing priority of event ring

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Message-ID: <YNSZZhGSZ0lFgS+U@kroah.com>
Date:   Thu, 24 Jun 2021 16:40:38 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        loic.poulain@...aro.org
Subject: Re: [PATCH 6/8] bus: mhi: core: Add support for processing priority
 of event ring

On Thu, Jun 24, 2021 at 07:54:53PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Jun 24, 2021 at 03:53:33PM +0200, Greg KH wrote:
> > On Mon, Jun 21, 2021 at 09:46:14PM +0530, Manivannan Sadhasivam wrote:
> > > From: Hemant Kumar <hemantk@...eaurora.org>
> > > 
> > > Event ring priorities are currently set to 1 and are unused.
> > > Default processing priority for event rings is set to regular
> > > tasklet. Controllers can choose to use high priority tasklet
> > > scheduling for certain event rings critical for processing such
> > > as ones transporting control information if they wish to avoid
> > > system scheduling delays for those packets. In order to support
> > > these use cases, allow controllers to set event ring priority to
> > > high.
> > > 
> > > Signed-off-by: Hemant Kumar <hemantk@...eaurora.org>
> > > Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
> > > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > Link: https://lore.kernel.org/r/1624053903-24653-2-git-send-email-bbhatt@codeaurora.org
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > ---
> > >  drivers/bus/mhi/core/init.c | 3 +--
> > >  drivers/bus/mhi/core/main.c | 9 +++++++--
> > >  include/linux/mhi.h         | 2 +-
> > >  3 files changed, 9 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
> > > index c81b377fca8f..444676034bf0 100644
> > > --- a/drivers/bus/mhi/core/init.c
> > > +++ b/drivers/bus/mhi/core/init.c
> > > @@ -673,8 +673,7 @@ static int parse_ev_cfg(struct mhi_controller *mhi_cntrl,
> > >  				&mhi_cntrl->mhi_chan[mhi_event->chan];
> > >  		}
> > >  
> > > -		/* Priority is fixed to 1 for now */
> > > -		mhi_event->priority = 1;
> > > +		mhi_event->priority = event_cfg->priority;
> > >  
> > >  		mhi_event->db_cfg.brstmode = event_cfg->mode;
> > >  		if (MHI_INVALID_BRSTMODE(mhi_event->db_cfg.brstmode))
> > > diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> > > index 8ac73f9e92a6..3775c77dec63 100644
> > > --- a/drivers/bus/mhi/core/main.c
> > > +++ b/drivers/bus/mhi/core/main.c
> > > @@ -454,10 +454,15 @@ irqreturn_t mhi_irq_handler(int irq_number, void *dev)
> > >  
> > >  		if (mhi_dev)
> > >  			mhi_notify(mhi_dev, MHI_CB_PENDING_DATA);
> > > -	} else {
> > > -		tasklet_schedule(&mhi_event->task);
> > > +
> > > +		return IRQ_HANDLED;
> > >  	}
> > >  
> > > +	if (!mhi_event->priority)
> > > +		tasklet_hi_schedule(&mhi_event->task);
> > > +	else
> > > +		tasklet_schedule(&mhi_event->task);
> > > +
> > >  	return IRQ_HANDLED;
> > >  }
> > >  
> > > diff --git a/include/linux/mhi.h b/include/linux/mhi.h
> > > index 86cea5256e3c..bf23c213429c 100644
> > > --- a/include/linux/mhi.h
> > > +++ b/include/linux/mhi.h
> > > @@ -250,7 +250,7 @@ struct mhi_channel_config {
> > >   * @irq_moderation_ms: Delay irq for additional events to be aggregated
> > >   * @irq: IRQ associated with this ring
> > >   * @channel: Dedicated channel number. U32_MAX indicates a non-dedicated ring
> > > - * @priority: Priority of this ring. Use 1 for now
> > > + * @priority: Processing priority of this ring. 0 is high and 1 is regular
> > 
> > Why is 0 high and 1 low?  Does that feel backwards?
> > 
> 
> That's because, "1" was used from the beginning by the controller drivers
> as the regular priority. And I thought of using "0" as high priority so
> that we can leave the controller drivers unmodified.

There's no problem modifying everyone, how much work is that?

> > Shouldn't this be a boolean, or if not, an enumerated type so that
> > people can read the code over time?
> > 
> 
> Bhaumik proposed an enum but I wanted 0/1 so that the controller drivers
> can be untouched. Also, I don't see any immediate requirement for other
> priorities.
> 
> Will make it a bool then.

Rename it when you change it so that you know you catch all existing
users.

thanks,

greg k-h