From 95c33ae41b822c37dc841cf80ca388fea376e36d Mon Sep 17 00:00:00 2001 From: Jeffrey Hugo Date: Mon, 18 Apr 2022 11:18:47 -0600 Subject: bus: mhi: host: Add soc_reset sysfs 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 Reviewed-by: Bhaumik Bhatt Reviewed-by: Manivannan Sadhasivam Link: https://lore.kernel.org/r/1650302327-30439-1-git-send-email-quic_jhugo@quicinc.com Signed-off-by: Manivannan Sadhasivam --- Documentation/ABI/stable/sysfs-bus-mhi | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'Documentation/ABI') diff --git a/Documentation/ABI/stable/sysfs-bus-mhi b/Documentation/ABI/stable/sysfs-bus-mhi index ecfe7662f8d0..96ccc3385a2b 100644 --- a/Documentation/ABI/stable/sysfs-bus-mhi +++ b/Documentation/ABI/stable/sysfs-bus-mhi @@ -19,3 +19,13 @@ 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. -- cgit v1.2.3