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Date:   Wed, 9 Sep 2020 22:08:38 +0000
From:   rishabhb@codeaurora.org
To:     Mathieu Poirier <mathieu.poirier@linaro.org>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org,
        tsoni@codeaurora.org, psodagud@codeaurora.org,
        sidgup@codeaurora.org, linux-remoteproc-owner@vger.kernel.org,
        kernel-team@android.com
Subject: Re: [PATCH v2 0/3] Expose recovery/coredump configuration from sysfs
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+android kernel team

On 2020-09-09 10:27, rishabhb@codeaurora.org wrote:
> 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
>>> > >