On Thu, Mar 13, 2025 at 05:10:14PM +0530, Krishna Chaitanya Chundru wrote:
> As per MHI spec sec 14, MHI supports bandwidth scaling to reduce power
Same here, add spec version.
> consumption. MHI bandwidth scaling is advertised in devices that contain
'advertised in devices or by devices'? Difference is subtle, but it changes the
context.
> 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
So this means both host and device has to support bandwidth scaling events? What
does 'events' mean here?
> 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.
>
Sounds like the host is depending on the device for bandwidth scaling.
> 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.
>
Why the controller driver needs to be involved for a spec defined feature?
This is not answered here.
> Add a new get_misc_doorbell() to get doorbell for misc capabilities to
> use the doorbell with mhi events like MHI BW scale etc.
>
So this is a spare doorbell? Why can't you call it as 'get_bw_scaling_db()'?
> 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@xxxxxxxxxxxxxxxx>
> ---
> drivers/bus/mhi/common.h | 16 +++++++
> drivers/bus/mhi/host/init.c | 64 ++++++++++++++++++++++++-
> drivers/bus/mhi/host/internal.h | 7 ++-
> drivers/bus/mhi/host/main.c | 101 +++++++++++++++++++++++++++++++++++++++-
> drivers/bus/mhi/host/pm.c | 10 +++-
> include/linux/mhi.h | 13 ++++++
> 6 files changed, 205 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
> index eedac801b800..0a02acee709a 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))
> +
> +#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 0b14b665ed15..71abe02f5726 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 */
Then open code in the caller itself. I see no benefit in adding it as a separate
function.
> +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, MHI_BW_SCALE_CAP_ID,
> + &bw_cfg_offset);
> + if (ret)
> + return ret;
> +
> + /* No ER configured to support BW scale */
What does it mean?
> + 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. Event ring:%d\n",
> + er_index);
> +
"Bandwidth scaling setup complete with event ring: %d\n"
> + 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 +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");
"Failed to setup bandwidth scaling: %d"
> + }
> 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;
bw_scaling_work or bw_scale_work?
> + struct mutex mutex;
Add a comment on the purpose of the 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..967563d86aec 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);
To avoid the hassle, I think it is worth changing the mutex in bwctrl to
spinlock. I don't think there would be issues in spinning inside
pcie_set_target_speed().
> + else
> + tasklet_schedule(&mhi_event->task);
> }
>
> return IRQ_HANDLED;
> @@ -1049,6 +1052,102 @@ 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;
exit_bw_scale?
> + }
> +
> + 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 */
Nit: Use caps for starting letter and also for acronyms.
> + 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);
dev_dbg()
> +
> + /* 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_dbg(dev, "exit er_index:%u ret:%d\n", mhi_event->er_index, ret);
Can these entry exit debug sequences be avoided?
- Mani
--
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