Re: [PATCH v1 1/4] bus: mhi: core: Add support for processing priority of event ring

[Manivannan Sadhasivam]

On Thu, Jun 17, 2021 at 02:30:32PM -0700, Bhaumik Bhatt 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
> with system scheduling delays for those packets. In order to
> support these use cases, allow controllers to set event ring
> priority to high. This patch only adds support and does not
> enable usage of these priorities.
> 
> Signed-off-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
> Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> ---
>  drivers/bus/mhi/core/internal.h |  2 +-
>  drivers/bus/mhi/core/main.c     | 19 ++++++++++++++++---
>  include/linux/mhi.h             | 14 ++++++++++++--
>  3 files changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
> index 672052f..666e102 100644
> --- a/drivers/bus/mhi/core/internal.h
> +++ b/drivers/bus/mhi/core/internal.h
> @@ -535,7 +535,7 @@ struct mhi_event {
>  	u32 intmod;
>  	u32 irq;
>  	int chan; /* this event ring is dedicated to a channel (optional) */
> -	u32 priority;
> +	enum mhi_er_priority priority;

Instead of using enum for priorities, can we just make use of the
existing "priority" field? Since the existing controllers set it to "1",
can we use "0" as the high priority?

This way we don't need to change the controller drivers.

>  	enum mhi_er_data_type data_type;
>  	struct mhi_ring ring;
>  	struct db_cfg db_cfg;
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 8ac73f9..bfc9776 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -425,10 +425,11 @@ void mhi_create_devices(struct mhi_controller *mhi_cntrl)
>  	}
>  }
>  
> -irqreturn_t mhi_irq_handler(int irq_number, void *dev)
> +irqreturn_t mhi_irq_handler(int irq_number, void *priv)
>  {
> -	struct mhi_event *mhi_event = dev;
> +	struct mhi_event *mhi_event = priv;
>  	struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
> +	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>  	struct mhi_event_ctxt *er_ctxt =
>  		&mhi_cntrl->mhi_ctxt->er_ctxt[mhi_event->er_index];
>  	struct mhi_ring *ev_ring = &mhi_event->ring;
> @@ -454,8 +455,20 @@ irqreturn_t mhi_irq_handler(int irq_number, void *dev)
>  
>  		if (mhi_dev)
>  			mhi_notify(mhi_dev, MHI_CB_PENDING_DATA);
> -	} else {
> +
> +		return IRQ_HANDLED;
> +	}
> +
> +	switch (mhi_event->priority) {
> +	case MHI_ER_PRIORITY_HI:

This could be,

	/* Use high priority tasklet for high priority event ring */
	if (!mhi_event->priority)
		tasklet_hi_schedule(&mhi_event->task);
	else
		tasklet_schedule(&mhi_event->task);

Thanks,
Mani

> +		tasklet_hi_schedule(&mhi_event->task);
> +		break;
> +	case MHI_ER_PRIORITY_DEFAULT:
>  		tasklet_schedule(&mhi_event->task);
> +		break;
> +	default:
> +		dev_err(dev, "Skip event of unknown priority\n");
> +		break;
>  	}
>  
>  	return IRQ_HANDLED;
> diff --git a/include/linux/mhi.h b/include/linux/mhi.h
> index 86cea52..25ee312 100644
> --- a/include/linux/mhi.h
> +++ b/include/linux/mhi.h
> @@ -198,6 +198,16 @@ enum mhi_er_data_type {
>  };
>  
>  /**
> + * enum mhi_er_priority - Event ring processing priority
> + * @MHI_ER_PRIORITY_HI: processed by hi-priority tasklet
> + * @MHI_ER_PRIORITY_DEFAULT: processed by regular tasklet
> + */
> +enum mhi_er_priority {
> +	MHI_ER_PRIORITY_HI,
> +	MHI_ER_PRIORITY_DEFAULT,
> +};
> +
> +/**
>   * enum mhi_db_brst_mode - Doorbell mode
>   * @MHI_DB_BRST_DISABLE: Burst mode disable
>   * @MHI_DB_BRST_ENABLE: Burst mode enable
> @@ -250,7 +260,7 @@ 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.
>   * @mode: Doorbell mode
>   * @data_type: Type of data this ring will process
>   * @hardware_event: This ring is associated with hardware channels
> @@ -262,7 +272,7 @@ struct mhi_event_config {
>  	u32 irq_moderation_ms;
>  	u32 irq;
>  	u32 channel;
> -	u32 priority;
> +	enum mhi_er_priority priority;
>  	enum mhi_db_brst_mode mode;
>  	enum mhi_er_data_type data_type;
>  	bool hardware_event;
> -- 
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>