Re: [PATCH v4 03/11] bus: mhi: host: Add support to read MHI capabilities

[Manivannan Sadhasivam <mani@kernel.org>]

On Mon, Jun 09, 2025 at 04:21:24PM GMT, Krishna Chaitanya Chundru wrote:
> From: Vivek Pernamitta <quic_vpernami@quicinc.com>
> 
> As per MHI spec v1.2,sec 6.6, MHI has capability registers which are
> located after the ERDB array. The location of this group of registers is
> indicated by the MISCOFF register. Each capability has a capability ID to
> determine which functionality is supported and each capability will point
> to the next capability supported.
> 
> Add a basic function to read those capabilities offsets.
> 
> Signed-off-by: Vivek Pernamitta <quic_vpernami@quicinc.com>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
> ---
>  drivers/bus/mhi/common.h    | 13 +++++++++++++
>  drivers/bus/mhi/host/init.c | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
> index dda340aaed95a5573a2ec776ca712e11a1ed0b52..58f27c6ba63e3e6fa28ca48d6d1065684ed6e1dd 100644
> --- a/drivers/bus/mhi/common.h
> +++ b/drivers/bus/mhi/common.h
> @@ -16,6 +16,7 @@
>  #define MHICFG				0x10
>  #define CHDBOFF				0x18
>  #define ERDBOFF				0x20
> +#define MISCOFF				0x24
>  #define BHIOFF				0x28
>  #define BHIEOFF				0x2c
>  #define DEBUGOFF			0x30
> @@ -113,6 +114,9 @@
>  #define MHISTATUS_MHISTATE_MASK		GENMASK(15, 8)
>  #define MHISTATUS_SYSERR_MASK		BIT(2)
>  #define MHISTATUS_READY_MASK		BIT(0)
> +#define MISC_CAP_MASK			GENMASK(31, 0)
> +#define CAP_CAPID_MASK			GENMASK(31, 24)
> +#define CAP_NEXT_CAP_MASK		GENMASK(23, 12)
>  
>  /* Command Ring Element macros */
>  /* No operation command */
> @@ -204,6 +208,15 @@
>  #define MHI_RSCTRE_DATA_DWORD1		cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
>  							       MHI_PKT_TYPE_COALESCING))
>  
> +enum mhi_capability_type {
> +	MHI_CAP_ID_INTX = 0x1,
> +	MHI_CAP_ID_TIME_SYNC = 0x2,
> +	MHI_CAP_ID_BW_SCALE = 0x3,
> +	MHI_CAP_ID_TSC_TIME_SYNC = 0x4,
> +	MHI_CAP_ID_MAX_TRB_LEN = 0x5,
> +	MHI_CAP_ID_MAX,
> +};
> +
>  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 13e7a55f54ff45b83b3f18b97e2cdd83d4836fe3..9102ce13a2059f599b46d25ef631f643142642be 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -467,6 +467,40 @@ int mhi_init_dev_ctxt(struct mhi_controller *mhi_cntrl)
>  	return ret;
>  }
>  
> +static int mhi_find_capability(struct mhi_controller *mhi_cntrl, u32 capability, u32 *offset)
> +{
> +	u32 val, cur_cap, next_offset;
> +	int ret;
> +
> +	/* Get the first supported capability offset */
> +	ret = mhi_read_reg_field(mhi_cntrl, mhi_cntrl->regs, MISCOFF, MISC_CAP_MASK, offset);
> +	if (ret)
> +		return ret;
> +
> +	*offset = (__force u32)le32_to_cpu(*offset);

Why do you need __force attribute? What does it suppress? Is it because the
pointer is not le32?

- Mani

> +	do {
> +		if (*offset >= mhi_cntrl->reg_len)
> +			return -ENXIO;
> +
> +		ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, *offset, &val);
> +		if (ret)
> +			return ret;
> +
> +		val = (__force u32)le32_to_cpu(val);
> +		cur_cap = FIELD_GET(CAP_CAPID_MASK, val);
> +		next_offset = FIELD_GET(CAP_NEXT_CAP_MASK, val);
> +		if (cur_cap >= MHI_CAP_ID_MAX)
> +			return -ENXIO;
> +
> +		if (cur_cap == capability)
> +			return 0;
> +
> +		*offset = next_offset;
> +	} while (next_offset);
> +
> +	return -ENXIO;
> +}
> +
>  int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
>  {
>  	u32 val;
> 
> -- 
> 2.34.1
> 

-- 
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