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Date: Wed, 21 Feb 2024 11:16:48 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Jeffrey Hugo <quic_jhugo@quicinc.com>
Cc: mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Revert "bus: mhi: core: Add support for reading MHI info
 from device"
Message-ID: <20240221054648.GD11693@thinkpad>
References: <20240219180748.1591527-1-quic_jhugo@quicinc.com>
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In-Reply-To: <20240219180748.1591527-1-quic_jhugo@quicinc.com>

On Mon, Feb 19, 2024 at 11:07:48AM -0700, Jeffrey Hugo wrote:
> This reverts commit 3316ab2b45f6bf4797d8d65b22fda3cc13318890.
> 
> The MHI spec owner pointed out that the SOC_HW_VERSION register is part
> of the BHIe segment, and only valid on devices which implement BHIe.
> Only a small subset of MHI devices implement BHIe so blindly accessing
> the register for all devices is not correct. Also, since the BHIe
> segment offset is not used when accessing the register, any
> implementation which moves the BHIe segment will result in accessing
> some other register.  We've seen that accessing this register on AIC100
> which does not support BHIe can result in initialization failures.
> 
> We could try to put checks into the code to address these issues, but in
> the roughly 4 years this functionality has existed, no one has used it.
> Easier to drop this dead code and address the issues if anyone comes up
> with a real world use for it.
> 
> Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

- Mani

> ---
>  drivers/bus/mhi/host/init.c     | 12 ------------
>  drivers/bus/mhi/host/internal.h |  6 ------
>  include/linux/mhi.h             | 17 -----------------
>  3 files changed, 35 deletions(-)
> 
> diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
> index 944da46e6f11..44f934981de8 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -914,7 +914,6 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
>  	struct mhi_chan *mhi_chan;
>  	struct mhi_cmd *mhi_cmd;
>  	struct mhi_device *mhi_dev;
> -	u32 soc_info;
>  	int ret, i;
>  
>  	if (!mhi_cntrl || !mhi_cntrl->cntrl_dev || !mhi_cntrl->regs ||
> @@ -989,17 +988,6 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl,
>  		mhi_cntrl->unmap_single = mhi_unmap_single_no_bb;
>  	}
>  
> -	/* Read the MHI device info */
> -	ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs,
> -			   SOC_HW_VERSION_OFFS, &soc_info);
> -	if (ret)
> -		goto err_destroy_wq;
> -
> -	mhi_cntrl->family_number = FIELD_GET(SOC_HW_VERSION_FAM_NUM_BMSK, soc_info);
> -	mhi_cntrl->device_number = FIELD_GET(SOC_HW_VERSION_DEV_NUM_BMSK, soc_info);
> -	mhi_cntrl->major_version = FIELD_GET(SOC_HW_VERSION_MAJOR_VER_BMSK, soc_info);
> -	mhi_cntrl->minor_version = FIELD_GET(SOC_HW_VERSION_MINOR_VER_BMSK, soc_info);
> -
>  	mhi_cntrl->index = ida_alloc(&mhi_controller_ida, GFP_KERNEL);
>  	if (mhi_cntrl->index < 0) {
>  		ret = mhi_cntrl->index;
> diff --git a/drivers/bus/mhi/host/internal.h b/drivers/bus/mhi/host/internal.h
> index 091244cf17c6..5fe49311b8eb 100644
> --- a/drivers/bus/mhi/host/internal.h
> +++ b/drivers/bus/mhi/host/internal.h
> @@ -15,12 +15,6 @@ extern struct bus_type mhi_bus_type;
>  #define MHI_SOC_RESET_REQ_OFFSET			0xb0
>  #define MHI_SOC_RESET_REQ				BIT(0)
>  
> -#define SOC_HW_VERSION_OFFS				0x224
> -#define SOC_HW_VERSION_FAM_NUM_BMSK			GENMASK(31, 28)
> -#define SOC_HW_VERSION_DEV_NUM_BMSK			GENMASK(27, 16)
> -#define SOC_HW_VERSION_MAJOR_VER_BMSK			GENMASK(15, 8)
> -#define SOC_HW_VERSION_MINOR_VER_BMSK			GENMASK(7, 0)
> -
>  struct mhi_ctxt {
>  	struct mhi_event_ctxt *er_ctxt;
>  	struct mhi_chan_ctxt *chan_ctxt;
> diff --git a/include/linux/mhi.h b/include/linux/mhi.h
> index 474d32cb0520..77b8c0a26674 100644
> --- a/include/linux/mhi.h
> +++ b/include/linux/mhi.h
> @@ -320,10 +320,6 @@ struct mhi_controller_config {
>   * @hw_ev_rings: Number of hardware event rings
>   * @sw_ev_rings: Number of software event rings
>   * @nr_irqs: Number of IRQ allocated by bus master (required)
> - * @family_number: MHI controller family number
> - * @device_number: MHI controller device number
> - * @major_version: MHI controller major revision number
> - * @minor_version: MHI controller minor revision number
>   * @serial_number: MHI controller serial number obtained from BHI
>   * @mhi_event: MHI event ring configurations table
>   * @mhi_cmd: MHI command ring configurations table
> @@ -368,15 +364,6 @@ struct mhi_controller_config {
>   * Fields marked as (required) need to be populated by the controller driver
>   * before calling mhi_register_controller(). For the fields marked as (optional)
>   * they can be populated depending on the usecase.
> - *
> - * The following fields are present for the purpose of implementing any device
> - * specific quirks or customizations for specific MHI revisions used in device
> - * by the controller drivers. The MHI stack will just populate these fields
> - * during mhi_register_controller():
> - *  family_number
> - *  device_number
> - *  major_version
> - *  minor_version
>   */
>  struct mhi_controller {
>  	struct device *cntrl_dev;
> @@ -407,10 +394,6 @@ struct mhi_controller {
>  	u32 hw_ev_rings;
>  	u32 sw_ev_rings;
>  	u32 nr_irqs;
> -	u32 family_number;
> -	u32 device_number;
> -	u32 major_version;
> -	u32 minor_version;
>  	u32 serial_number;
>  
>  	struct mhi_event *mhi_event;
> -- 
> 2.34.1
> 

-- 
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