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Message-ID: <d6ae3572-58db-5264-c26a-9f75de6292a7@quicinc.com>
Date:   Wed, 13 Apr 2022 15:54:55 -0700
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Subject: Re: [PATCH v2] bus: mhi: host: Add soc_reset sysfs
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To:     Jeffrey Hugo <quic_jhugo@quicinc.com>, <mani@kernel.org>,
        <quic_hemantk@quicinc.com>
CC:     <mhi@lists.linux.dev>, <linux-arm-msm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Jeffrey Hugo <jhugo@codeaurora.org>
References: <1649883619-17609-1-git-send-email-quic_jhugo@quicinc.com>
From:   Bhaumik Vasav Bhatt <quic_bbhatt@quicinc.com>
In-Reply-To: <1649883619-17609-1-git-send-email-quic_jhugo@quicinc.com>
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On 4/13/2022 2:00 PM, Jeffrey Hugo wrote:
> From: Jeffrey Hugo <jhugo@codeaurora.org>
>
> The MHI bus supports a standardized hardware reset, which is known as the
> "SoC Reset".  This reset is similar to the reset sysfs for PCI devices -
> a hardware mechanism to reset the state back to square one.
>
> The MHI SoC Reset is described in the spec as a reset of last resort.  If
> some unrecoverable error has occurred where other resets have failed, SoC
> Reset is the "big hammer" that ungracefully resets the device.  This is
> effectivly the same as yanking the power on the device, and reapplying it.
> However, depending on the nature of the particular issue, the underlying
> transport link may remain active and configured.  If the link remains up,
> the device will flag a MHI system error early in the boot process after
> the reset is executed, which allows the MHI bus to process a fatal error
> event, and clean up appropiately.
>
> While the SoC Reset is generally intended as a means of recovery when all
> else has failed, it can be useful in non-error scenarios.  For example,
> if the device loads firmware from the host filesystem, the device may need
> to be fully rebooted inorder to pick up the new firmware.  In this
> scenario, the system administrator may use the soc_reset sysfs to cause
> the device to pick up the new firmware that the admin placed on the
> filesystem.
>
> Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
> Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
> ---
Reviewed-by: Bhaumik Bhatt <quic_bbhatt@quicinc.com>
> v2:
> Rebase
>
>   Documentation/ABI/stable/sysfs-bus-mhi | 11 +++++++++++
>   drivers/bus/mhi/host/init.c            | 14 ++++++++++++++
>   2 files changed, 25 insertions(+)
>
> diff --git a/Documentation/ABI/stable/sysfs-bus-mhi b/Documentation/ABI/stable/sysfs-bus-mhi
> index ecfe766..306f63e 100644
> --- a/Documentation/ABI/stable/sysfs-bus-mhi
> +++ b/Documentation/ABI/stable/sysfs-bus-mhi
> @@ -19,3 +19,14 @@ Description:	The file holds the OEM PK Hash value of the endpoint device
>   		read without having the device power on at least once, the file
>   		will read all 0's.
>   Users:		Any userspace application or clients interested in device info.
> +
> +What:           /sys/bus/mhi/devices/.../soc_reset
> +Date:           April 2022
> +KernelVersion:  5.19
> +Contact:        mhi@lists.linux.dev
> +Description:	Initiates a SoC reset on the MHI controller.  A SoC reset is
> +                a reset of last resort, and will require a complete re-init.
> +                This can be useful as a method of recovery if the device is
> +                non-responsive, or as a means of loading new firmware as a
> +                system administration task.
> +
> diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
> index 04c409b..e12b210 100644
> --- a/drivers/bus/mhi/host/init.c
> +++ b/drivers/bus/mhi/host/init.c
> @@ -108,9 +108,23 @@ static ssize_t oem_pk_hash_show(struct device *dev,
>   }
>   static DEVICE_ATTR_RO(oem_pk_hash);
>   
> +static ssize_t soc_reset_store(struct device *dev,
> +			       struct device_attribute *attr,
> +			       const char *buf,
> +			       size_t count)
> +{
> +	struct mhi_device *mhi_dev = to_mhi_device(dev);
> +	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
> +
> +	mhi_soc_reset(mhi_cntrl);
> +	return count;
> +}
> +static DEVICE_ATTR_WO(soc_reset);
> +
>   static struct attribute *mhi_dev_attrs[] = {
>   	&dev_attr_serial_number.attr,
>   	&dev_attr_oem_pk_hash.attr,
> +	&dev_attr_soc_reset.attr,
>   	NULL,
>   };
>   ATTRIBUTE_GROUPS(mhi_dev);