Date:   Wed, 9 Sep 2020 17:27:45 +0000
From:   rishabhb@...eaurora.org
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        tsoni@...eaurora.org, psodagud@...eaurora.org,
        sidgup@...eaurora.org, linux-remoteproc-owner@...r.kernel.org
Subject: Re: [PATCH v2 0/3] Expose recovery/coredump configuration from sysfs

On 2020-09-04 15:02, Mathieu Poirier wrote:
> On Thu, Sep 03, 2020 at 06:59:44PM -0500, Bjorn Andersson wrote:
>> On Tue 01 Sep 17:05 CDT 2020, Mathieu Poirier wrote:
>> 
>> > Hi Rishabh,
>> >
>> > On Thu, Aug 27, 2020 at 12:48:48PM -0700, 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. This patch series adds a configurable option
>> > > to move the recovery/coredump interfaces to sysfs. If the feature
>> > > flag is selected it would move these interfaces to sysfs and remove
>> > > the equivalent debugfs interface.
>> >
>> > What I meant wast to move the coredump entry from debugfs to sysfs and from
>> > there make it available to user space using a kernel config.
>> 
>> Why would we not always make this available in sysfs?
> 
> At this time the options are in debugfs and vendors can decide to make 
> that
> available on products if they want to.  The idea behind using a kernel
> configuration once moved to sysfs was to give the same kind of options.
> 
>> 
>> > But thinking further on this it may be better to simply provide an API
>> > to set the coredump mode from the platform driver, the same way
>> > rproc_coredump_set_elf_info() works.
>> 
>> Being able to invoke these from the platform drivers sounds like a new
>> feature. What would trigger the platform drivers to call this? Or are
>> you perhaps asking for the means of the drivers to be able to select 
>> the
>> default mode?
> 
> My ultimate goal is to avoid needlessly stuffing things in sysfs.  My 
> hope in
> suggesting a new API was that platform drivers could recognise the kind 
> of
> build/environment they operate in and setup the coredump mode 
> accordingly.  That
> would have allowed us to leave debugfs options alone.
> 
>> 
>> Regarding the default mode, I think it would make sense to make the
>> default "disabled", because this is the most sensible configuration in 
>> a
>> "production" environment. And the sysfs means we have a convenient
>> mechanism to configure it, even on production environments.
>> 
> 
> I am weary of changing something that hasn't been requested.
> 
>> > That will prevent breaking a fair amount of user space code...
>> >
>> 
>> We typically don't guarantee that the debugfs interfaces are stable 
>> and
>> if I understand the beginning of you reply you still want to move it
>> from debugfs to sysfs - which I presume would break such scripts in 
>> the
>> first place?
> 
> Correct - I am sure that moving coredump and recovery options to sysfs 
> will
> break user space scripts.  Even if debugfs is not part of the ABI it 
> would be
> nice to avoid disrupting people as much as possible.
> 
>> 
>> 
>> I would prefer to see that we don't introduce config options for every
>> little thing, unless there's good reason for it.
> 
> I totally agree.  It is with great reluctance that I asked Rishab to 
> proceed
> the way he did in V3.  His usecase makes sense... On the flip side this 
> is
> pushed down on the kernel community and I really like Christoph's 
> position about
> fixing Android and leaving the kernel alone.
> 
Well, removing debugfs is conscious decision taken by android due to 
security
concerns and there is not we can fix there.
Would it be a terrible idea to have recovery and coredump exposed from 
both
sysfs and debugfs instead of choosing one and breaking userspace code?
>> 
>> Regards,
>> Bjorn
>> 
>> > Let me know if that can work for you.
>> >
>> > Thanks,
>> > Mathieu
>> >
>> > > '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 build
>> > > and "disabled" in production builds. Whereas recovery needs to be
>> > > "disabled" for debugging purposes and "enabled" on production builds.
>> > >
>> > > Changelog:
>> > >
>> > > 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: Expose remoteproc configuration through sysfs
>> > >   remoteproc: Add coredump configuration to sysfs
>> > >   remoteproc: Add recovery configuration to sysfs
>> > >
>> > >  Documentation/ABI/testing/sysfs-class-remoteproc |  44 ++++++++
>> > >  drivers/remoteproc/Kconfig                       |  12 +++
>> > >  drivers/remoteproc/remoteproc_debugfs.c          |  10 +-
>> > >  drivers/remoteproc/remoteproc_sysfs.c            | 126 +++++++++++++++++++++++
>> > >  4 files changed, 190 insertions(+), 2 deletions(-)
>> > >
>> > > --
>> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> > > a Linux Foundation Collaborative Project
>> > >

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