RE: [PATCH v3] i2c: imx: mark I2C adapter when hardware is powered down

["Carlos Song (OSS)" <carlos.song@oss.nxp.com>]

> -----Original Message-----
> From: Mukesh Savaliya <mukesh.savaliya@oss.qualcomm.com>
> Sent: Thursday, May 21, 2026 7:14 PM
> To: Carlos Song (OSS) <carlos.song@oss.nxp.com>; Mukesh Savaliya
> <mukesh.savaliya@oss.qualcomm.com>; o.rempel@pengutronix.de;
> kernel@pengutronix.de; andi.shyti@kernel.org; Frank Li <frank.li@nxp.com>;
> s.hauer@pengutronix.de; festevam@gmail.com; Carlos Song
> <carlos.song@nxp.com>; Bough Chen <haibo.chen@nxp.com>
> Cc: linux-i2c@vger.kernel.org; imx@lists.linux.dev;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> stable@vger.kernel.org
> Subject: Re: [PATCH v3] i2c: imx: mark I2C adapter when hardware is powered
> down
> 
> 
> On 5/21/2026 4:21 PM, Carlos Song (OSS) wrote:
> 
> [...]
> 
> >>>> -----Original Message-----
> >>>> From: Mukesh Savaliya <mukesh.savaliya@oss.qualcomm.com>
> >>>> Sent: Thursday, May 21, 2026 3:40 PM
> >>>> To: Carlos Song (OSS) <carlos.song@oss.nxp.com>;
> >>>> o.rempel@pengutronix.de; kernel@pengutronix.de;
> >>>> andi.shyti@kernel.org; Frank Li <frank.li@nxp.com>;
> >>>> s.hauer@pengutronix.de; festevam@gmail.com; Carlos Song
> >>>> <carlos.song@nxp.com>; Bough Chen <haibo.chen@nxp.com>
> >>>> Cc: linux-i2c@vger.kernel.org; imx@lists.linux.dev;
> >>>> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> >>>> stable@vger.kernel.org
> >>>> Subject: Re: [PATCH v3] i2c: imx: mark I2C adapter when hardware is
> >>>> powered down
> >>>>
> >>>> Hi Carlos,
> >>>>
> >>>> On 5/20/2026 3:45 PM, Carlos Song (OSS) wrote:
> >>>>> From: Carlos Song <carlos.song@nxp.com>
> >>>>>
> >>>>> Mark the I2C adapter as suspended during system suspend to block
> >>>>> further transfers, and resume it on system resume. This prevents
> >>>>> potential hangs when the hardware is powered down but clients
> >>>>> still attempt
> >>>> I2C transfers.
> >>>>>
> >> what was the reason of this hang ? I was thinking you don't have
> >> interrupts working when client requested transfer but adapter was
> >> suspended. Please correct me if wrong.
> >>
> >> And it would be good to mention the actual problem and why/how it
> occurred.
> >>>> Code changes looks fine to me but have comment on commit log.
> >>>>
> >>>> It seems, you are adding support of _noirq() callbacks to allow
> >>>> transfers during suspend/resume noirq phase of PM.
> >>>>
> >>>> Would it make sense if you can write "Replace system PM callbacks
> >>>> with noirq PM callbacks" OR "Allow transfers during _noirq phase of
> >>>> the PM ops" instead of "mark I2C adapter when hardware is powered
> >> down" ?
> >>>>
> >>>
> >>> Hi,
> >>>
> >>> Thank you for your comments!
> >>>
> >>> But this patch is added is not for support noirq PM callback or
> >>> transfer in noirq
> >> phase.
> >>>
> >> Okay, may be actual problem description can help me.
> >>> In fact, this fix is to mark the I2C adapter as suspended during
> >>> system noirq suspend to block further transfers, and resume it on
> >>> system noirq resume. This is to prohibit I2C device calling the I2C
> >>> controller after the system noirq suspend and before noirq resume,
> >>> because at
> >> this time the I2C instance is powered off or the clock is disabled
> >> ... So I want to keep current commit. How do you think?
> >> completely Makes sense. Please help add how this problem occurred and
> why ?
> >> So the change/fix will be good to understand against it.
> >
> > Hi,
> >
> > In some I.MX platform, some I2C devices will keep a work queue all
> > time, the work queue will trigger I2C xfer every once in a while, but the work
> queue shouldn't be free in system suspend.
> >
> 
> work queue has transfers queued even if system is suspended ? IMO, the client
> i2c devices should not let system go to suspend.
> 

Hi Mukesh,

Thank you for the detailed discussion.

Yes, I totally agree that I2C client drivers should ideally stop
issuing transfers when the system is suspending.

However, in practice there are many different I2C clients, and not all
of them strictly adhere to this requirement. Some clients may still
trigger transfers through workqueues or deferred contexts during the
suspend/resume window.

Therefore, adding this protection at the I2C controller side helps to
avoid unexpected accesses when the hardware resources are unavailable,
making the system more robust.

> > Within a very short time window, possibly from noirq_suspend to the
> > system actually being suspended, or possibly from the system starting
> > to resume to before noirq_resume, this work queue will trigger an I2C
> > transfer, and at this time the I2C controller's clk and pinctrl have
> > not yet been restored, reading and
> 
> Right, this kind of explains the problem to me. I think you are trying to serve
> i2c transfers when your resources(clk, pinctrl) are not turned ON and also
> interrupt remains disabled. And that's why you need to add
> _noir() PM callbacks supports along with IRQF_NO_SUSPEND |
> IRQF_EARLY_RESUME flags.
> 
> > writing I2C registers causes the system to hang. This patch make all
> > I2C operations are performed in a safe hardware state.
> >
> > Is it better if I add these comment to patch commit log?
> >>>
> if my latest comments makes sense against the issue, you may write
> accordingly. if i am wrong, then your explanation makes sense. Cause of the
> hang needs to be clearly mention int the commit log in your next patch.
> 

Based on our discussion, I have updated the commit log as below:

On some i.MX platforms, certain I2C client drivers keep a periodic
workqueue which continues to trigger I2C transfers.

During system suspend/resume, there exists a time window between:
  - noirq_suspend and full suspend
  - resume start and noirq_resume

In this window, the I2C controller resources such as clock and pinctrl
may already be disabled or not yet restored.

If a workqueue triggers an I2C transfer in this period, the driver
attempts to access I2C registers while the hardware resources are
unavailable, which may lead to system hang.

Mark the I2C adapter as suspended during noirq suspend and block new
transfers until resume, ensuring that I2C transfers are only issued
when hardware resources are available.

Does this look good to you?

> >>
> >