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

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Wed, 9 Jul 2025, Krishna Chaitanya Chundru wrote:
> On 7/8/2025 10:06 PM, Manivannan Sadhasivam wrote:
> > 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?
> > 
> yes to suppress warnings.

I'm pretty sure sparce with endianness checking won't be happy with that 
construct as you pass u32 where le32_to_cpu() expects __le32. Have you 
checked this with sparse? (It might not check endianness with default args.)

> > > +	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;
> > > +}

There's a generalization of capability search in Hans Zhang's series, 
can it be used here too?


-- 
 i.