linux-kernel - Re: [PATCH] bus: mhi: host: Add sysfs entry to force device to enter EDL

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Date: Tue, 2 Jan 2024 22:22:29 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Jeffrey Hugo <quic_jhugo@...cinc.com>
Cc: Qiang Yu <quic_qianyu@...cinc.com>, mhi@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	quic_cang@...cinc.com, quic_mrana@...cinc.com,
	Bhaumik Bhatt <quic_bbhatt@...cinc.com>
Subject: Re: [PATCH] bus: mhi: host: Add sysfs entry to force device to enter
 EDL

On Tue, Jan 02, 2024 at 08:31:15AM -0700, Jeffrey Hugo wrote:
> On 12/25/2023 12:47 AM, Qiang Yu wrote:
> > From: Bhaumik Bhatt <quic_bbhatt@...cinc.com>
> > 
> > Forcing the device (eg. SDX75) to enter Emergency Download Mode involves
> > writing the 0xEDEDEDED cookie to the channel 91 doorbell register and
> > forcing an SOC reset afterwards. Allow users of the MHI bus to exercise the
> > sequence using a sysfs entry.
> 
> I don't see this documented in the spec anywhere.  Is this standard behavior
> for all MHI devices?
> 
> What about devices that don't support EDL mode?
> 
> How should the host avoid using this special cookie when EDL mode is not
> desired?
> 

All points raised by Jeff are valid. I had discussions with Hemant and Bhaumik
previously on allowing the devices to enter EDL mode in a generic manner and we
didn't conclude on one final approach.

Whatever way we come up with, it should be properly described in the MHI spec
and _should_ be backwards compatible.

- Mani

> -Jeff

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