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

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Date: Tue, 9 Jan 2024 16:43:13 +0800
From: Qiang Yu <quic_qianyu@...cinc.com>
To: Jeffrey Hugo <quic_jhugo@...cinc.com>, <mani@...nel.org>
CC: <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 1/2/2024 11:31 PM, 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?

This is documented in MHI spec v1.2, 13.2 Emergency download (EDL) mode 
cookie. So I think

it is standard behavior. At least, SDX65 and SDX75 support it.

>
> What about devices that don't support EDL mode?
>
> How should the host avoid using this special cookie when EDL mode is 
> not desired?

Can I include another flag in mhi_pci_dev_info and mhi_controller and 
check this flag

before writing EDL cookie?

>
> -Jeff