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

[Greg KH]

On Mon, Jun 21, 2021 at 09:46:14PM +0530, Manivannan Sadhasivam wrote:
> From: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/1624053903-24653-2-git-send-email-bbhatt@xxxxxxxxxxxxxx
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> ---
>  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?

Shouldn't this be a boolean, or if not, an enumerated type so that
people can read the code over time?

thanks,

greg k-h