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    SubjectRe: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time
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    29.04.2020 19:54, Dmitry Osipenko пишет:
    > 29.04.2020 19:30, Thierry Reding пишет:
    >> On Wed, Apr 29, 2020 at 03:35:26PM +0300, Dmitry Osipenko wrote:
    >>> 29.04.2020 11:55, Thierry Reding пишет:
    >>> ...
    >>>>>> It's not "papering over an issue". The bug can't be fixed properly
    >>>>>> without introducing I2C atomic transfers support for a late suspend
    >>>>>> phase, I don't see any other solutions for now. Stable kernels do not
    >>>>>> support atomic transfers at all, that proper solution won't be backportable.
    >>>>>
    >>>>> Hm... on a hunch I tried something and, lo and behold, it worked. I can
    >>>>> get Cardhu to properly suspend/resume on top of v5.7-rc3 with the
    >>>>> following sequence:
    >>>>>
    >>>>> revert 9f42de8d4ec2 i2c: tegra: Fix suspending in active runtime PM state
    >>>>> apply http://patchwork.ozlabs.org/project/linux-tegra/patch/20191213134417.222720-1-thierry.reding@gmail.com/
    >>>>>
    >>>>> I also ran that through our test farm and I don't see any other issues.
    >>>>> At the time I was already skeptical about pm_runtime_force_suspend() and
    >>>>> pm_runtime_force_resume() and while I'm not fully certain why exactly it
    >>>>> doesn't work, the above on top of v5.7-rc3 seems like a good option.
    >>>>>
    >>>>> I'll try to do some digging if I can find out why exactly force suspend
    >>>>> and resume doesn't work.
    >>>>
    >>>> Ah... so it looks like pm_runtime_force_resume() never actually does
    >>>> anything in this case and then disable_depth remains at 1 and the first
    >>>> tegra_i2c_xfer() will then fail to runtime resume the controller.
    >>>
    >>> That's the exactly expected behaviour of the RPM force suspend/resume.
    >>> The only unexpected part for me is that the tegra_i2c_xfer() runtime
    >>> resume then fails in the NOIRQ phase.
    >>>
    >>> Anyways, again, today it's wrong to use I2C in the NOIRQ phase becasue
    >>> I2C interrupt is disabled. It's the PCIe driver that should be fixed.
    >>
    >> I don't think so. Everything works perfectly fine if we fix system
    >> suspend/resume not to rely on pm_runtime_force_{suspend,resume}() and
    >> directly call the runtime suspend/resume implementations.
    >
    > It should "work" only in conjunction with my I2C patch, otherwise you'll
    > get a spurious I2C timeout error. And it will "work" only because
    > interrupt is handled manually after the timeout, meaning that yours
    > suspending time will take few hundreds ms more.
    >
    >> So can we please stop deflecting and fix the damn I2C driver. From my
    >> perspective we have two choices:
    >>
    >> 1) do what I suggested above and revert the force suspend/resume patch
    >> and apply the "manual" suspend/resume patch instead
    >>
    >> 2) revert this patch and go back to the drawing board
    >>
    >> I suspect that with 2) we'd end up back where we started and have to do
    >> 1) anyway.
    >>
    >> An alternative that I'd prefer even more would be to do 2) now for v5.7
    >> and then we do 1) for v5.8 and give this some more soaking time.
    >
    > I2C driver isn't broken, PCIe driver is. IMO.
    >
    > Both yours variants are not going to be a backportable fix for the
    > stable kernels, they won't fix the suspended interrupt problem. What I'm
    > missing?
    >

    My proposal:

    1. Fix PCIe driver by keeping regulator always-ON, propagate it to
    stable kernels.

    2. Make I2C driver usable in NOIRQ phase.

    3. Make PCIe driver to handle errors properly.

    4. Revert the PCIe driver "fix".

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