Message-ID: <92e70ba0-a83f-bcfd-8579-840da59c5f90@oss.qualcomm.com>
Date: Wed, 19 Feb 2025 23:32:59 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Jingoo Han <jingoohan1@...il.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        Jeff Johnson <jjohnson@...nel.org>, linux-pci@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, linux-arm-msm@...r.kernel.org,
        mhi@...ts.linux.dev, linux-wireless@...r.kernel.org,
        ath11k@...ts.infradead.org, quic_jjohnson@...cinc.com,
        quic_pyarlaga@...cinc.com, quic_vbadigan@...cinc.com,
        quic_vpernami@...cinc.com, quic_mrana@...cinc.com
Subject: Re: [PATCH 6/8] bus: mhi: host: Add support for Bandwidth scale



On 2/17/2025 2:47 PM, Ilpo Järvinen wrote:
> On Mon, 17 Feb 2025, Krishna Chaitanya Chundru wrote:
> 
>> As per MHI spec sec 14, MHI supports bandwidth scaling to reduce power
>> consumption. MHI bandwidth scaling is advertised in devices that contain
>> the bandwidth scaling capability registers. If enabled, the device
>> aggregates bandwidth requirements and sends them to the host in the form
>> of an event. After the host performs the bandwidth switch, it sends an
>> acknowledgment by ringing a doorbell.
>>
>> if the host supports bandwidth scaling events, then it must set
>> BW_CFG.ENABLED bit, set BW_CFG.DB_CHAN_ID to the channel ID to the
>> doorbell that will be used by the host to communicate the bandwidth
>> scaling status and BW_CFG.ER_INDEX to the index for the event ring
>> to which the device should send bandwidth scaling request in the
>> bandwidth scaling capability register.
>>
>> As part of mmio init check if the bw scale capability is present or not,
>> if present advertise host supports bw scale by setting all the required
>> fields.
>>
>> MHI layer will only forward the bw scaling request to the controller
>> driver, it is responsibility of the controller driver to do actual bw
>> scaling and then pass status to the MHI. MHI will response back to the
>> device based up on the status of the bw scale received.
>>
>> Add a new get_misc_doorbell() to get doorbell for misc capabilities to
>> use the doorbell with mhi events like MHI BW scale etc.
>>
>> Use workqueue & mutex for the bw scale events as the pci_set_target_speed()
>> which will called by the mhi controller driver can sleep.
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
>> ---
>>   drivers/bus/mhi/common.h        |  14 ++++++
>>   drivers/bus/mhi/host/init.c     |  64 ++++++++++++++++++++++++-
>>   drivers/bus/mhi/host/internal.h |   7 ++-
>>   drivers/bus/mhi/host/main.c     | 102 +++++++++++++++++++++++++++++++++++++++-
>>   drivers/bus/mhi/host/pm.c       |  10 +++-
>>   include/linux/mhi.h             |  13 +++++
>>   6 files changed, 204 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
>> index eedac801b800..b900199fab10 100644
>> --- a/drivers/bus/mhi/common.h
>> +++ b/drivers/bus/mhi/common.h
>> @@ -208,6 +208,20 @@
>>   #define MHI_RSCTRE_DATA_DWORD1		cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
>>   							       MHI_PKT_TYPE_COALESCING))
>>   
>> +/* MHI Bandwidth scaling offsets */
>> +#define BW_SCALE_CFG_OFFSET		(0x04)
>> +#define BW_SCALE_CFG_CHAN_DB_ID_SHIFT	(25)
>> +#define BW_SCALE_CFG_ENABLED_MASK	BIT(24)
>> +#define BW_SCALE_CFG_ENABLED_SHIFT	(24)
>> +#define BW_SCALE_CFG_ER_ID_SHIFT	(19)
>> +
>> +#define BW_SCALE_CAP_ID			(3)
>> +#define MHI_TRE_GET_EV_BW_REQ_SEQ(tre)	(((tre)->dword[0] >> 8) & 0xFF)
> 
> This looks open-coded FIELD_GET(). Add the field define and use
> FIELD_GET() with it.
> 
ack
>> +
>> +#define MHI_BW_SCALE_RESULT(status, seq)	(((status) & 0xF) << 8 | \
>> +						((seq) & 0xFF))
> 
> 2x FIELD_PREP().
> 
ack
>> +#define	MHI_BW_SCALE_NACK			0xF
>> +
>>   enum mhi_pkt_type {
>>   	MHI_PKT_TYPE_INVALID = 0x0,
>>   	MHI_PKT_TYPE_NOOP_CMD = 0x1,
>> diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
>> index 0b14b665ed15..f15c79f85d13 100644
>> --- a/drivers/bus/mhi/host/init.c
>> +++ b/drivers/bus/mhi/host/init.c
>> @@ -496,10 +496,56 @@ static int mhi_get_capability_offset(struct mhi_controller *mhi_cntrl, u32 capab
>>   	return -ENXIO;
>>   }
>>   
>> +/* to be used only if a single event ring with the type is present */
>> +static int mhi_get_er_index(struct mhi_controller *mhi_cntrl,
>> +			    enum mhi_er_data_type type)
>> +{
>> +	struct mhi_event *mhi_event = mhi_cntrl->mhi_event;
>> +	int i;
>> +
>> +	/* find event ring for requested type */
>> +	for (i = 0; i < mhi_cntrl->total_ev_rings; i++, mhi_event++) {
>> +		if (mhi_event->data_type == type)
>> +			return mhi_event->er_index;
>> +	}
>> +
>> +	return -ENOENT;
>> +}
>> +
>> +static int mhi_init_bw_scale(struct mhi_controller *mhi_cntrl,
>> +			     int bw_scale_db)
>> +{
>> +	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>> +	u32 bw_cfg_offset, val = 0;
>> +	int ret, er_index;
>> +
>> +	ret = mhi_get_capability_offset(mhi_cntrl, BW_SCALE_CAP_ID,
>> +					&bw_cfg_offset);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* No ER configured to support BW scale */
>> +	er_index = mhi_get_er_index(mhi_cntrl, MHI_ER_BW_SCALE);
>> +	if (er_index < 0)
>> +		return er_index;
>> +
>> +	bw_cfg_offset += BW_SCALE_CFG_OFFSET;
>> +
>> +	/* advertise host support */
>> +	val = ((bw_scale_db << BW_SCALE_CFG_CHAN_DB_ID_SHIFT) |
>> +		BW_SCALE_CFG_ENABLED_MASK | (er_index << BW_SCALE_CFG_ER_ID_SHIFT));
> 
> Please name the fields with defines and use FIELD_PREP(). And remove
> _SHIFT ending defines.
> 
> Also make the file does correct #include for FIELD_PREP/GET if not yet
> there.
> 
ack
>> +	mhi_write_reg(mhi_cntrl, mhi_cntrl->regs, bw_cfg_offset, val);
>> +
>> +	dev_info(dev, "Bandwidth scaling setup complete. Event ring:%d\n",
>> +		 er_index);
> 
> This sound like dev_dbg() to me. What's the value for user in normal
> scenarios?
> 
ack
>> +	return 0;
>> +}
>> +
>>   int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
>>   {
>>   	u32 val;
>> -	int i, ret;
>> +	int i, ret, doorbell;
>>   	struct mhi_chan *mhi_chan;
>>   	struct mhi_event *mhi_event;
>>   	void __iomem *base = mhi_cntrl->regs;
>> @@ -633,6 +679,16 @@ int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
>>   		return ret;
>>   	}
>>   
>> +	if (mhi_cntrl->get_misc_doorbell)
>> +		doorbell = mhi_cntrl->get_misc_doorbell(mhi_cntrl, MHI_ER_BW_SCALE);
>> +
>> +	if (doorbell > 0) {
>> +		ret = mhi_init_bw_scale(mhi_cntrl, doorbell);
>> +		if (!ret)
>> +			mhi_cntrl->bw_scale_db = base + val + (8 * doorbell);
>> +		else
>> +			dev_warn(dev, "BW scale setup failure\n");
> 
> Is it okay to return 0 in this case?
> 
Not all the controllers support this feature, so we want to return
failure so that controllers can continue normally.
>> +	}
>>   	return 0;
>>   }
>>   
>> @@ -778,6 +834,9 @@ static int parse_ev_cfg(struct mhi_controller *mhi_cntrl,
>>   		case MHI_ER_CTRL:
>>   			mhi_event->process_event = mhi_process_ctrl_ev_ring;
>>   			break;
>> +		case MHI_ER_BW_SCALE:
>> +			mhi_event->process_event = mhi_process_bw_scale_ev_ring;
>> +			break;
>>   		default:
>>   			dev_err(dev, "Event Ring type not supported\n");
>>   			goto error_ev_cfg;
>> @@ -1012,9 +1071,12 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
>>   
>>   		mhi_event->mhi_cntrl = mhi_cntrl;
>>   		spin_lock_init(&mhi_event->lock);
>> +		mutex_init(&mhi_event->mutex);
>>   		if (mhi_event->data_type == MHI_ER_CTRL)
>>   			tasklet_init(&mhi_event->task, mhi_ctrl_ev_task,
>>   				     (ulong)mhi_event);
>> +		else if (mhi_event->data_type == MHI_ER_BW_SCALE)
>> +			INIT_WORK(&mhi_event->work, mhi_process_ev_work);
>>   		else
>>   			tasklet_init(&mhi_event->task, mhi_ev_task,
>>   				     (ulong)mhi_event);
>> diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
>> index 3134f111be35..bf7c6a7c9383 100644
>> --- a/drivers/bus/mhi/host/internal.h
>> +++ b/drivers/bus/mhi/host/internal.h
>> @@ -241,6 +241,8 @@ struct mhi_event {
>>   	struct mhi_ring ring;
>>   	struct db_cfg db_cfg;
>>   	struct tasklet_struct task;
>> +	struct work_struct work;
>> +	struct mutex mutex;
>>   	spinlock_t lock;
>>   	int (*process_event)(struct mhi_controller *mhi_cntrl,
>>   			     struct mhi_event *mhi_event,
>> @@ -403,7 +405,8 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>>   				struct mhi_event *mhi_event, u32 event_quota);
>>   int mhi_process_ctrl_ev_ring(struct mhi_controller *mhi_cntrl,
>>   			     struct mhi_event *mhi_event, u32 event_quota);
>> -
>> +int mhi_process_bw_scale_ev_ring(struct mhi_controller *mhi_cntrl,
>> +				 struct mhi_event *mhi_event, u32 event_quota);
>>   /* ISR handlers */
>>   irqreturn_t mhi_irq_handler(int irq_number, void *dev);
>>   irqreturn_t mhi_intvec_threaded_handler(int irq_number, void *dev);
>> @@ -419,5 +422,5 @@ void mhi_unmap_single_no_bb(struct mhi_controller *mhi_cntrl,
>>   			    struct mhi_buf_info *buf_info);
>>   void mhi_unmap_single_use_bb(struct mhi_controller *mhi_cntrl,
>>   			     struct mhi_buf_info *buf_info);
>> -
>> +void mhi_process_ev_work(struct work_struct *work);
>>   #endif /* _MHI_INT_H */
>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
>> index 4de75674f193..a6732bbead44 100644
>> --- a/drivers/bus/mhi/host/main.c
>> +++ b/drivers/bus/mhi/host/main.c
>> @@ -472,7 +472,10 @@ 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);
>> +		if (mhi_event->data_type == MHI_ER_BW_SCALE)
>> +			queue_work(mhi_cntrl->hiprio_wq, &mhi_event->work);
>> +		else
>> +			tasklet_schedule(&mhi_event->task);
>>   	}
>>   
>>   	return IRQ_HANDLED;
>> @@ -1049,6 +1052,103 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
>>   	return count;
>>   }
>>   
>> +/* dedicated bw scale event ring processing */
>> +int mhi_process_bw_scale_ev_ring(struct mhi_controller *mhi_cntrl,
>> +				 struct mhi_event *mhi_event, u32 event_quota)
>> +{
>> +	struct mhi_event_ctxt *er_ctxt = &mhi_cntrl->mhi_ctxt->er_ctxt[mhi_event->er_index];
>> +	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>> +	struct mhi_ring *ev_ring = &mhi_event->ring;
>> +	dma_addr_t ptr = le64_to_cpu(er_ctxt->rp);
>> +	u32 response = MHI_BW_SCALE_NACK;
>> +	struct mhi_ring_element *dev_rp;
>> +	struct mhi_link_info link_info;
>> +	int ret = -EINVAL;
>> +
>> +	if (unlikely(MHI_EVENT_ACCESS_INVALID(mhi_cntrl->pm_state))) {
>> +		ret =  -EIO;
>> +		goto exit_bw_scale_process;
>> +	}
>> +
>> +	if (!MHI_IN_MISSION_MODE(mhi_cntrl->ee))
>> +		goto exit_bw_scale_process;
>> +
>> +	if (!is_valid_ring_ptr(ev_ring, ptr)) {
>> +		dev_err(dev,
>> +			"Event ring rp points outside of the event ring\n");
>> +		ret =  -EIO;
>> +		goto exit_bw_scale_process;
>> +	}
>> +
>> +	dev_rp = mhi_to_virtual(ev_ring, ptr);
>> +
>> +	/* if rp points to base, we need to wrap it around */
>> +	if (dev_rp == ev_ring->base)
>> +		dev_rp = ev_ring->base + ev_ring->len;
>> +	dev_rp--;
>> +
>> +	/* fast forward to currently processed element and recycle er */
>> +	ev_ring->rp = dev_rp;
>> +	ev_ring->wp = dev_rp - 1;
>> +	if (ev_ring->wp < ev_ring->base)
>> +		ev_ring->wp = ev_ring->base + ev_ring->len - ev_ring->el_size;
>> +	mhi_recycle_ev_ring_element(mhi_cntrl, ev_ring);
>> +
>> +	if (WARN_ON(MHI_TRE_GET_EV_TYPE(dev_rp) != MHI_PKT_TYPE_BW_REQ_EVENT)) {
>> +		dev_err(dev, "!BW SCALE REQ event\n");
>> +		goto exit_bw_scale_process;
>> +	}
>> +
>> +	link_info.target_link_speed = MHI_TRE_GET_EV_LINKSPEED(dev_rp);
>> +	link_info.target_link_width = MHI_TRE_GET_EV_LINKWIDTH(dev_rp);
>> +	link_info.sequence_num = MHI_TRE_GET_EV_BW_REQ_SEQ(dev_rp);
>> +
>> +	dev_info(dev, "Received BW_REQ with seq:%d link speed:0x%x width:0x%x\n",
>> +		 link_info.sequence_num,
>> +		 link_info.target_link_speed,
>> +		 link_info.target_link_width);
>> +
>> +	/* bring host and device out of suspended states */
>> +	ret = mhi_device_get_sync(mhi_cntrl->mhi_dev);
>> +	if (ret)
>> +		goto exit_bw_scale_process;
>> +
>> +	mhi_cntrl->runtime_get(mhi_cntrl);
>> +
>> +	ret = mhi_cntrl->bw_scale(mhi_cntrl, &link_info);
>> +	if (!ret)
>> +		response = 0;
>> +
>> +	response = MHI_BW_SCALE_RESULT(response, link_info.sequence_num);
>> +
>> +	write_lock_bh(&mhi_cntrl->pm_lock);
>> +	mhi_write_reg(mhi_cntrl, mhi_cntrl->bw_scale_db, 0, response);
>> +	write_unlock_bh(&mhi_cntrl->pm_lock);
>> +
>> +	mhi_cntrl->runtime_put(mhi_cntrl);
>> +	mhi_device_put(mhi_cntrl->mhi_dev);
>> +
>> +exit_bw_scale_process:
>> +	dev_info(dev, "exit er_index:%u ret:%d\n", mhi_event->er_index, ret);
> 
> There's zero value for normal user with something as obscure as
> this, make it dev_dbg().
> 
ack
>> +	return ret;
>> +}
>> +
>> +void mhi_process_ev_work(struct work_struct *work)
>> +{
>> +	struct mhi_event *mhi_event = container_of(work, struct mhi_event,
>> +						   work);
>> +
>> +	struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
>> +
>> +	if (unlikely(MHI_EVENT_ACCESS_INVALID(mhi_cntrl->pm_state)))
>> +		return;
>> +
>> +	mutex_lock(&mhi_event->mutex);
> 
> guard()()
> 
ack.

- Krishna Chaitanya.
>> +	mhi_event->process_event(mhi_cntrl, mhi_event, U32_MAX);
>> +	mutex_unlock(&mhi_event->mutex);
>> +}
>> +
>>   void mhi_ev_task(unsigned long data)
>>   {
>>   	struct mhi_event *mhi_event = (struct mhi_event *)data;
>> diff --git a/drivers/bus/mhi/host/pm.c b/drivers/bus/mhi/host/pm.c
>> index 11c0e751f223..9c848ca582f0 100644
>> --- a/drivers/bus/mhi/host/pm.c
>> +++ b/drivers/bus/mhi/host/pm.c
>> @@ -523,7 +523,10 @@ static void mhi_pm_disable_transition(struct mhi_controller *mhi_cntrl,
>>   		if (mhi_event->offload_ev)
>>   			continue;
>>   		disable_irq(mhi_cntrl->irq[mhi_event->irq]);
>> -		tasklet_kill(&mhi_event->task);
>> +		if (mhi_event->data_type == MHI_ER_BW_SCALE)
>> +			cancel_work_sync(&mhi_event->work);
>> +		else
>> +			tasklet_kill(&mhi_event->task);
>>   	}
>>   
>>   	/* Release lock and wait for all pending threads to complete */
>> @@ -670,7 +673,10 @@ static void mhi_pm_sys_error_transition(struct mhi_controller *mhi_cntrl)
>>   	for (i = 0; i < mhi_cntrl->total_ev_rings; i++, mhi_event++) {
>>   		if (mhi_event->offload_ev)
>>   			continue;
>> -		tasklet_kill(&mhi_event->task);
>> +		if (mhi_event->data_type == MHI_ER_BW_SCALE)
>> +			cancel_work_sync(&mhi_event->work);
>> +		else
>> +			tasklet_kill(&mhi_event->task);
>>   	}
>>   
>>   	/* Release lock and wait for all pending threads to complete */
>> diff --git a/include/linux/mhi.h b/include/linux/mhi.h
>> index 059dc94d20bb..d9bf88c35d14 100644
>> --- a/include/linux/mhi.h
>> +++ b/include/linux/mhi.h
>> @@ -102,10 +102,12 @@ struct image_info {
>>    * struct mhi_link_info - BW requirement
>>    * target_link_speed - Link speed as defined by TLS bits in LinkControl reg
>>    * target_link_width - Link width as defined by NLW bits in LinkStatus reg
>> + * sequence_num - used by device to track bw requests sent to host
>>    */
>>   struct mhi_link_info {
>>   	unsigned int target_link_speed;
>>   	unsigned int target_link_width;
>> +	int sequence_num;
>>   };
>>   
>>   /**
>> @@ -183,10 +185,12 @@ enum mhi_ch_ee_mask {
>>    * enum mhi_er_data_type - Event ring data types
>>    * @MHI_ER_DATA: Only client data over this ring
>>    * @MHI_ER_CTRL: MHI control data and client data
>> + * @MHI_ER_BW_SCALE: MHI controller bandwidth scale functionality
>>    */
>>   enum mhi_er_data_type {
>>   	MHI_ER_DATA,
>>   	MHI_ER_CTRL,
>> +	MHI_ER_BW_SCALE,
>>   };
>>   
>>   /**
>> @@ -299,6 +303,7 @@ struct mhi_controller_config {
>>    * @bhi: Points to base of MHI BHI register space
>>    * @bhie: Points to base of MHI BHIe register space
>>    * @wake_db: MHI WAKE doorbell register address
>> + * @wake_db: MHI BW_SCALE doorbell register address
>>    * @iova_start: IOMMU starting address for data (required)
>>    * @iova_stop: IOMMU stop address for data (required)
>>    * @fw_image: Firmware image name for normal booting (optional)
>> @@ -355,6 +360,8 @@ struct mhi_controller_config {
>>    * @write_reg: Write a MHI register via the physical link (required)
>>    * @reset: Controller specific reset function (optional)
>>    * @edl_trigger: CB function to trigger EDL mode (optional)
>> + * @get_misc_doobell: function to get doorbell used for MISC feature like BW scale etc (optional)
>> + * @bw_scale: CB function for passing BW scale info (optional)
>>    * @buffer_len: Bounce buffer length
>>    * @index: Index of the MHI controller instance
>>    * @bounce_buf: Use of bounce buffer
>> @@ -376,6 +383,7 @@ struct mhi_controller {
>>   	void __iomem *bhi;
>>   	void __iomem *bhie;
>>   	void __iomem *wake_db;
>> +	void __iomem *bw_scale_db;
>>   
>>   	dma_addr_t iova_start;
>>   	dma_addr_t iova_stop;
>> @@ -440,6 +448,11 @@ struct mhi_controller {
>>   	void (*reset)(struct mhi_controller *mhi_cntrl);
>>   	int (*edl_trigger)(struct mhi_controller *mhi_cntrl);
>>   
>> +	int (*get_misc_doorbell)(struct mhi_controller *mhi_cntrl,
>> +				 enum mhi_er_data_type type);
>> +	int (*bw_scale)(struct mhi_controller *mhi_cntrl,
>> +			struct mhi_link_info *link_info);
>> +
>>   	size_t buffer_len;
>>   	int index;
>>   	bool bounce_buf;
>>
>>
> 

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