linux-kernel - Re: [PATCH v6 0/3] Move recovery/coredump configuration to sysfs

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Date:   Tue, 29 Sep 2020 19:18:31 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Rishabh Bhatnagar <rishabhb@...eaurora.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tsoni@...eaurora.org" <tsoni@...eaurora.org>,
        "psodagud@...eaurora.org" <psodagud@...eaurora.org>,
        "sidgup@...eaurora.org" <sidgup@...eaurora.org>
Subject: Re: [PATCH v6 0/3] Move recovery/coredump configuration to sysfs



On 9/29/20 4:33 PM, Bjorn Andersson wrote:
> On Tue 29 Sep 03:44 CDT 2020, Arnaud POULIQUEN wrote:
> 
>>
>>
>> On 9/29/20 12:17 AM, Rishabh Bhatnagar wrote:
>>> From Android R onwards Google has restricted access to debugfs in user
>>> and user-debug builds. This restricts access to most of the features
>>> exposed through debugfs. 'Coredump' and 'Recovery' are critical
>>> interfaces that are required for remoteproc to work on Qualcomm Chipsets. 
>>> Coredump configuration needs to be set to "inline" in debug/test builds
>>> and "disabled" in production builds. Whereas recovery needs to be
>>> "disabled" for debugging purposes and "enabled" on production builds.
>>> This patch series removes the recovery/coredump entries from debugfs
>>> and moves them to sysfs. Also, this disables the coredump collection
>>> by default as this is a requirement for production devices.
>>>
>>> Changelog:
>>>
>>> v6 -> v5:
>>> - Disable coredump collection by default
>>> - Rename the "default" configuration to "enabled" to avoid confusion
>>>
>>> v5 -> v4:
>>> - Fix the cover-letter of tha patch series.
>>>
>>> v4 -> v3:
>>> - Remove the feature flag to expose recovery/coredump
>>>
>>> v3 -> v2:
>>> - Remove the coredump/recovery entries from debugfs
>>
>> Sorry i missed this and some associated discussion in V2...
>>
>> I have also some concerns about the ABI breaks.
> 
> Debugfs is not an ABI...
> 
>> In ST and I suppose in several companies we have some 
>> test environments that use the debugfs to generate and/or get
>> the core dump.
>>
> 
> I do however acknowledge the inconvenience you're facing...
> 
>> Even if the stability of the debugfs is not guaranteed it would
>> be nice to keep both interface.
>>
> 
> ...and I wouldn't mind keeping the debugfs interface around, at least
> for some time to allow people to transition their tools/muscle memory.
> 
>> It seems that it is possible to create symbolic link in the debugfs
>> thanks to the "debugfs_create_symlink" function.
>> This seems allowing to keep files in both place without duplicating the code.
>> To be honest i have never used this function so I'm not 100% sure that this
>> would do the job...
>> But if you think that this could be a good compromise, i can test it.
>>
> 
> The duplicated code is rather simple, so I don't mind the duplication -
> for now.
> 
> 
> So, how about we add the sysfs pieces of Rishabh's patches, leave out
> the debugfs and then in a while (e.g. one LTS) we remove the debugfs
> code?

This smooth transition seems to me a very good compromise.

Thanks,
Arnaud

> 
> Regards,
> Bjorn
> 
>> Regards,
>> Arnaud
>>
>>> - Expose recovery/coredump from sysfs under a feature flag
>>>
>>> v1 -> v2:
>>> - Correct the contact name in the sysfs documentation.
>>> - Remove the redundant write documentation for coredump/recovery sysfs
>>> - Add a feature flag to make this interface switch configurable.
>>>
>>> Rishabh Bhatnagar (3):
>>>   remoteproc: Move coredump configuration to sysfs
>>>   remoteproc: Move recovery configuration to sysfs
>>>   remoteproc: Change default dump configuration to "disabled"
>>>
>>>  Documentation/ABI/testing/sysfs-class-remoteproc |  46 +++++++
>>>  drivers/remoteproc/remoteproc_coredump.c         |   6 +-
>>>  drivers/remoteproc/remoteproc_debugfs.c          | 168 -----------------------
>>>  drivers/remoteproc/remoteproc_sysfs.c            | 120 ++++++++++++++++
>>>  include/linux/remoteproc.h                       |   8 +-
>>>  5 files changed, 173 insertions(+), 175 deletions(-)
>>>