linux-kernel - Re: [PATCH v2 0/3] Expose recovery/coredump configuration from sysfs

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Message-ID: <41909da5-bc64-e81c-9a1d-99ab413461ec@st.com>
Date:   Tue, 29 Sep 2020 09:43:15 +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>,
        "mathieu.poirier@...aro.org" <mathieu.poirier@...aro.org>,
        "tsoni@...eaurora.org" <tsoni@...eaurora.org>,
        "psodagud@...eaurora.org" <psodagud@...eaurora.org>,
        "sidgup@...eaurora.org" <sidgup@...eaurora.org>
Subject: Re: [PATCH v2 0/3] Expose recovery/coredump configuration from sysfs

Hi Bjorn,

On 9/26/20 5:31 AM, Bjorn Andersson wrote:
> On Tue 15 Sep 02:51 PDT 2020, Arnaud POULIQUEN wrote:
> 
>> Hi Rishabh,
>>
>> On 8/27/20 9:48 PM, 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. '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.
>>
>> The remoteproc_cdev had been created to respond to some sysfs limitations.
> 
> The limitation here is in debugfs not being available on all systems,
> sysfs is present and I really do like the idea of being able to change
> these things without having to compile a tool to invoke the ioctl...

Right,

> 
>> I wonder if this evolution should not also be implemented in the cdev.
>> In this case an additional event could be addedd to inform the application
>> that a crash occurred and that a core dump is available.
>>
> 
> Specifically for userspace to know when a coredump is present there's
> already uevents being sent when the devcoredump is ready. That said,
> having some means to getting notified about remoteproc state changes
> does sounds reasonable. If there is a use case we should discuss that.

The main use case i have in mind is to inform the userspace that the remote
processor has crashed. This would allow applications to perform specific action
to avoid getting stuck and/or resetting it's environement befor restarting the
remote processor and associated IPC.
If i well remember QCOM has this kind of mechanism for its modem but this is
implemented in a platform driver.
We would be interested to have something more generic relying on the remoteproc
framework.

Thanks,
Arnaud

> 
>> Of course it's only a suggestion... As it would be a redesign.
> 
> A very valid suggestion. I don't think it's a redesign, but more of an
> extension of what we have today.
> 
> Regards,
> Bjorn
> 
>> I let Björn and Mathieu comment.
>>
>> Regards,
>> Arnaud
>>
>>>
>>> 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(-)
>>>