linux-kernel - Re: [PATCH 10/11] drivers: bus: mhi: host: Add support for MHI MAX TRB capability

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Message-ID: <gok5wlsti3y7eebdo4rjbvoclo3d2o2e3bseo3lwrooo5sf64a@42balu3tsz5e>
Date: Tue, 13 Jan 2026 13:57:42 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Sivareddy Surasani <sivareddy.surasani@....qualcomm.com>
Cc: Jonathan Corbet <corbet@....net>, Arnd Bergmann <arnd@...db.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
	Upal Kumar Saha <upal.saha@....qualcomm.com>, Himanshu Shukla <quic_himashuk@...cinc.com>, 
	Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>
Subject: Re: [PATCH 10/11] drivers: bus: mhi: host: Add support for MHI MAX
 TRB capability

On Thu, Dec 11, 2025 at 01:37:42PM +0530, Sivareddy Surasani wrote:
> From: Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>
> 
> Read the MHI capability for MAX TRB length if device is supporting.

Expand TRB.

> Use this information to send MHI data with a higher TRB length, as
> supported by the device.
> 

Add some context on what the device is going to do with it.

> Signed-off-by: Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>
> Signed-off-by: Sivareddy Surasani <sivareddy.surasani@....qualcomm.com>
> ---
>  drivers/bus/mhi/common.h    |  9 ++++++++-
>  drivers/bus/mhi/host/init.c | 21 +++++++++++++++++++++
>  drivers/bus/mhi/host/main.c | 17 ++++++++++++++---
>  include/linux/mhi.h         |  2 ++
>  4 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
> index 3b3ecbc6169f..4962035f4693 100644
> --- a/drivers/bus/mhi/common.h
> +++ b/drivers/bus/mhi/common.h
> @@ -158,6 +158,8 @@
>  #define MHI_TRE_GET_EV_PTR(tre)		le64_to_cpu((tre)->ptr)
>  #define MHI_TRE_GET_EV_CODE(tre)	FIELD_GET(GENMASK(31, 24), (MHI_TRE_GET_DWORD(tre, 0)))
>  #define MHI_TRE_GET_EV_LEN(tre)		FIELD_GET(GENMASK(15, 0), (MHI_TRE_GET_DWORD(tre, 0)))
> +#define MHI_TRE_GET_EV_LEN_MAX_TRB(max_trb, tre)    (GENMASK(__fls(max_trb), 0) & \
> +						    (MHI_TRE_GET_DWORD(tre, 0)))
>  #define MHI_TRE_GET_EV_CHID(tre)	FIELD_GET(GENMASK(31, 24), (MHI_TRE_GET_DWORD(tre, 1)))
>  #define MHI_TRE_GET_EV_TYPE(tre)	FIELD_GET(GENMASK(23, 16), (MHI_TRE_GET_DWORD(tre, 1)))
>  #define MHI_TRE_GET_EV_STATE(tre)	FIELD_GET(GENMASK(31, 24), (MHI_TRE_GET_DWORD(tre, 0)))
> @@ -188,6 +190,7 @@
>  /* Transfer descriptor macros */
>  #define MHI_TRE_DATA_PTR(ptr)		cpu_to_le64(ptr)
>  #define MHI_TRE_DATA_DWORD0(len)	cpu_to_le32(FIELD_PREP(GENMASK(15, 0), len))
> +#define MHI_TRE_DATA_DWORD0_MAX_TREB_CAP(max_len, len)	((GENMASK(__fls(max_len), 0)) & (len))
>  #define MHI_TRE_TYPE_TRANSFER		2
>  #define MHI_TRE_DATA_DWORD1(bei, ieot, ieob, chain) cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
>  								MHI_TRE_TYPE_TRANSFER) |    \
> @@ -206,7 +209,11 @@
>  #define MHI_RSCTRE_DATA_PTR(ptr, len)	cpu_to_le64(FIELD_PREP(GENMASK(64, 48), len) | ptr)
>  #define MHI_RSCTRE_DATA_DWORD0(cookie)	cpu_to_le32(cookie)
>  #define MHI_RSCTRE_DATA_DWORD1		cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
> -							       MHI_PKT_TYPE_COALESCING))
> +								MHI_PKT_TYPE_COALESCING))
> +
> +/* MHI Max TRB Length CAP ID */
> +#define MAX_TRB_LEN_CAP_ID		0x5
> +#define MAX_TRB_LEN_CFG			0x4
>  
>  enum mhi_capability_type {
>  	MHI_CAP_ID_INTX = 0x1,
> diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
> index 50f96f2c823f..b0982cb24fb9 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -500,6 +500,25 @@ static int mhi_find_capability(struct mhi_controller *mhi_cntrl, u32 capability,
>  	return -ENXIO;
>  }
>  
> +static int mhi_init_ext_trb_len(struct mhi_controller *mhi_cntrl)

Why _ext_?

> +{
> +	struct device *dev = &mhi_cntrl->mhi_dev->dev;
> +	u32 trb_offset;
> +	int ret;
> +
> +	ret = mhi_find_capability(mhi_cntrl, MAX_TRB_LEN_CAP_ID, &trb_offset);
> +	if (ret)
> +		return ret;
> +
> +	/* Get max TRB length */
> +	ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs,
> +			   trb_offset + MAX_TRB_LEN_CFG, &mhi_cntrl->ext_trb_len);
> +
> +	dev_dbg(dev, "Max TRB length supported is : 0x%x\n", mhi_cntrl->ext_trb_len);

"Max TRB length: 0x%x"

But it feels more natural to expose the value in decimal, than in hex.

- Mani

-- 
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