On Mon, 19 May 2025, Krishna Chaitanya Chundru wrote:
> As per MHI spec v1.2, sec 14, MHI supports bandwidth scaling to reduce
> power consumption. MHI bandwidth scaling is advertised by devices that
> contain the bandwidth scaling capability registers. If enabled, the device
> aggregates bandwidth requirements and sends them to the host through
> dedicated mhi event ring. 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 since MHI doesn't have any idea about transport layer used by
> the controller, 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.
>
> Co-developed-by: Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> Signed-off-by: Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
> ---
> drivers/bus/mhi/common.h | 16 +++++++
> drivers/bus/mhi/host/init.c | 61 ++++++++++++++++++++++++-
> drivers/bus/mhi/host/internal.h | 7 ++-
> drivers/bus/mhi/host/main.c | 98 ++++++++++++++++++++++++++++++++++++++++-
> drivers/bus/mhi/host/pm.c | 10 ++++-
> include/linux/mhi.h | 13 ++++++
> 6 files changed, 199 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
> index eedac801b80021e44f7c65d33cd50760e06c02f2..0a02acee709af7a2a6abddcb9547ef56564ce453 100644
> --- a/drivers/bus/mhi/common.h
> +++ b/drivers/bus/mhi/common.h
> @@ -208,6 +208,22 @@
> #define MHI_RSCTRE_DATA_DWORD1 cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
> MHI_PKT_TYPE_COALESCING))
>
> +/* MHI Bandwidth scaling offsets */
> +#define MHI_BW_SCALE_CFG_OFFSET 0x4
> +#define MHI_BW_SCALE_CAP_ID (3)
> +
> +#define MHI_BW_SCALE_ENABLE(bw_scale_db, er_index) cpu_to_le32(FIELD_PREP(GENMASK(31, 25), \
> + bw_scale_db) | \
> + FIELD_PREP(GENMASK(23, 19), er_index) | \
> + BIT(24))
This code would be easier to understand if you would name those
GENMASK()s and BIT() with defines first.
Why does this have to be a macro?
These are also hard to read when they're misindented like that.
> +#define MHI_TRE_GET_EV_BW_REQ_SEQ(tre) FIELD_GET(GENMASK(15, 8), (MHI_TRE_GET_DWORD(tre, 0)))
> +#define MHI_BW_SCALE_DB_ID(er_index) FIELD_PREP(GENMASK(31, 25), er_index)
> +
> +#define MHI_BW_SCALE_RESULT(status, seq) cpu_to_le32(FIELD_PREP(GENMASK(11, 8), status) | \
> + FIELD_PREP(GENMASK(7, 0), seq))
> +#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 a7137a040bdce1c58c98fe9c2340aae4cc4387d1..9fe6020f7868ec8bd114d0d96edc9d17624cbac5 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -496,10 +496,53 @@ static int mhi_find_capability(struct mhi_controller *mhi_cntrl, u32 capability,
> return -ENXIO;
> }
>
> +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;
> + int ret, er_index, val;
> + u32 bw_cfg_offset;
> +
> + ret = mhi_find_capability(mhi_cntrl, MHI_BW_SCALE_CAP_ID, &bw_cfg_offset);
> + if (ret)
> + return ret;
> +
> + er_index = mhi_get_er_index(mhi_cntrl, MHI_ER_BW_SCALE);
> + if (er_index < 0)
> + return er_index;
> +
> + bw_cfg_offset += MHI_BW_SCALE_CFG_OFFSET;
> +
> + /* Advertise host support */
> + val = MHI_BW_SCALE_ENABLE(bw_scale_db, er_index);
> +
> + mhi_write_reg(mhi_cntrl, mhi_cntrl->regs, bw_cfg_offset, val);
> +
> + dev_dbg(dev, "Bandwidth scaling setup complete with event ring: %d\n",
> + er_index);
> +
> + return 0;
> +}
> +
> int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
> {
> u32 val;
> - int i, ret;
> + int i, ret, doorbell = 0;
> struct mhi_chan *mhi_chan;
> struct mhi_event *mhi_event;
> void __iomem *base = mhi_cntrl->regs;
> @@ -633,6 +676,16 @@ 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, "Failed to setup bandwidth scaling: %d\n", ret);
> + }
> return 0;
> }
>
> @@ -778,6 +831,9 @@ 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 +1068,12 @@ 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 ce566f7d2e9240c64044407aa4124ad3cdb98003..cf64adaecad2aeec8569da5276ec60dd7e97e5e0 100644
> --- a/drivers/bus/mhi/host/internal.h
> +++ b/drivers/bus/mhi/host/internal.h
> @@ -248,6 +248,8 @@ struct mhi_event {
> struct mhi_ring ring;
> struct db_cfg db_cfg;
> struct tasklet_struct task;
> + struct work_struct work;
> + struct mutex mutex; /* lock for synchronization */
> spinlock_t lock;
> int (*process_event)(struct mhi_controller *mhi_cntrl,
> struct mhi_event *mhi_event,
> @@ -410,7 +412,8 @@ 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);
> @@ -426,5 +429,5 @@ 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 9bb0df43ceef1e54e8817422516aab1def6fdc4a..f87e9550b59227947fc7268c5799eea274c66b98 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 +1052,99 @@ int mhi_process_data_event_ring(struct mhi_controller *mhi_cntrl,
> return count;
> }
>
> +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;
> + }
> +
> + if (!MHI_IN_MISSION_MODE(mhi_cntrl->ee))
> + goto exit_bw_scale;
> +
> + 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;
> + }
> +
> + 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;
> + }
> +
> + 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_dbg(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;
> +
> + 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:
> + 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;
> +
> + guard(mutex)(&mhi_event->mutex);
> + mhi_event->process_event(mhi_cntrl, mhi_event, U32_MAX);
> +}
> +
> 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 2fb27e6f8f88ebc701dad56dd60844d8470dd418..8b518da4995d83a299f419908b3753e6b78c8803 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 dd372b0123a6da5107b807ff8fe940c567eb2030..2041bbb2e2396eb2e19e6bc0a5e981aa2917ebdd 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;
>
>
--
i.
