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

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Message-ID: <20200929143357.GE10036@builder.lan>
Date:   Tue, 29 Sep 2020 09:33:57 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@...com>
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 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?

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(-)
> >