[PATCH v5 4/6] bus: mhi: host: Add support for Bandwidth scale
Manivannan Sadhasivam
mani at kernel.org
Tue Sep 1 01:06:05 PDT 2026
On Wed, Aug 19, 2026 at 06:55:55PM +0530, 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 at oss.qualcomm.com>
> Signed-off-by: Qiang Yu <qiang.yu at oss.qualcomm.com>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru at oss.qualcomm.com>
> ---
> drivers/bus/mhi/common.h | 13 +++++
> drivers/bus/mhi/host/init.c | 93 +++++++++++++++++++++++++++++++--
> drivers/bus/mhi/host/internal.h | 6 ++-
> drivers/bus/mhi/host/main.c | 113 +++++++++++++++++++++++++++++++++++++++-
> drivers/bus/mhi/host/pm.c | 10 +++-
> drivers/bus/mhi/host/trace.h | 7 +++
> include/linux/mhi.h | 13 +++++
> 7 files changed, 247 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
> index 4c316f3d5a68..267260901a41 100644
> --- a/drivers/bus/mhi/common.h
> +++ b/drivers/bus/mhi/common.h
> @@ -215,6 +215,19 @@
> #define MHI_CAP_ID_MAX_TRB_LEN 0x5
> #define MHI_CAP_ID_MAX 0x6
>
> +/* MHI Bandwidth scaling offsets */
> +#define MHI_BW_SCALE_CFG_OFFSET 0x4
> +#define MHI_BW_SCALE_CAP_ID (3)
> +#define MHI_BW_SCALE_DB_CHAN_ID GENMASK(31, 25)
> +#define MHI_BW_SCALE_ENABLED BIT(24)
> +#define MHI_BW_SCALE_ER_INDEX GENMASK(23, 19)
> +
> +#define MHI_TRE_GET_EV_BW_REQ_SEQ(tre) FIELD_GET(GENMASK(15, 8), (MHI_TRE_GET_DWORD(tre, 0)))
> +
> +#define MHI_BW_SCALE_RESULT(status, seq) (FIELD_PREP(GENMASK(11, 8), status) | \
> + FIELD_PREP(GENMASK(7, 0), seq))
> +#define MHI_BW_SCALE_NACK 0xF
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 32db4aa4bbe8..d0975b6c2df0 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -497,10 +497,66 @@ static int mhi_find_capability(struct mhi_controller *mhi_cntrl, u32 capability)
> return 0;
> }
>
> +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;
> + struct mhi_event *mhi_event;
> + u32 bw_cfg_offset, val;
> + int er_index, i;
> +
> + bw_cfg_offset = mhi_find_capability(mhi_cntrl, MHI_BW_SCALE_CAP_ID);
> + if (!bw_cfg_offset)
> + return 0;
> +
> + er_index = mhi_get_er_index(mhi_cntrl, MHI_ER_BW_SCALE);
> + if (er_index < 0)
> + return er_index;
> +
> + /* Initialize BW scale event ring resources */
> + mhi_event = mhi_cntrl->mhi_event;
> + for (i = 0; i < mhi_cntrl->total_ev_rings; i++, mhi_event++) {
> + if (mhi_event->data_type == MHI_ER_BW_SCALE) {
> + INIT_WORK(&mhi_event->work, mhi_process_ev_work);
> + mutex_init(&mhi_event->mutex);
Why do you need mutex only for this event and not for other events?
> + break;
> + }
> + }
> +
> + bw_cfg_offset += MHI_BW_SCALE_CFG_OFFSET;
> +
> + /* Advertise host support */
> + val = FIELD_PREP(MHI_BW_SCALE_DB_CHAN_ID, bw_scale_db) |
> + FIELD_PREP(MHI_BW_SCALE_ER_INDEX, er_index) |
> + MHI_BW_SCALE_ENABLED;
> +
> + 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;
> + u32 val, chdb_offset;
> + int i, ret, doorbell = 0;
> struct mhi_chan *mhi_chan;
> struct mhi_event *mhi_event;
> void __iomem *base = mhi_cntrl->regs;
> @@ -581,6 +637,8 @@ int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
> return -ERANGE;
> }
>
> + chdb_offset = val;
> +
> /* Setup wake db */
> mhi_cntrl->wake_db = base + val + (8 * MHI_DEV_WAKE_DB);
> mhi_cntrl->wake_set = false;
> @@ -634,6 +692,17 @@ 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);
Why can't you add the doorbell number to 'mhi_event_config'?
> +
> + if (doorbell > 0) {
> + ret = mhi_init_bw_scale(mhi_cntrl, doorbell);
> + if (!ret)
> + mhi_cntrl->bw_scale_db = base + chdb_offset + (8 * doorbell);
> + else
> + dev_warn(dev, "Failed to setup bandwidth scaling: %d\n", ret);
> + }
> +
> return 0;
> }
>
> @@ -778,6 +847,9 @@ 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;
> @@ -1001,10 +1073,12 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
>
> mhi_event->mhi_cntrl = mhi_cntrl;
> spin_lock_init(&mhi_event->lock);
> - if (mhi_event->data_type == MHI_ER_CTRL)
> + if (mhi_event->data_type == MHI_ER_CTRL) {
> tasklet_init(&mhi_event->task, mhi_ctrl_ev_task,
> (ulong)mhi_event);
> - else
> + } else if (mhi_event->data_type == MHI_ER_BW_SCALE) {
> + /* BW scale resources will be initialized in mhi_init_mmio() if capability exists */
But you are just skipping the tasklet here. Provide an apt reason for that.
- Mani
--
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