Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver

[Sameer Pujar]

On 1/22/2020 9:57 PM, Dmitry Osipenko wrote:
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>
> 22.01.2020 14:52, Jon Hunter ÐÐÑÐÑ:
> > On 22/01/2020 07:16, Sameer Pujar wrote:
> >
> > ...
> >
> > > > > > > > > +static int tegra210_i2s_remove(struct platform_device *pdev)
> > > > > > > > > +{
> > > > > > > > > +     pm_runtime_disable(&pdev->dev);
> > > > > > > > > +     if (!pm_runtime_status_suspended(&pdev->dev))
> > > > > > > > > +             tegra210_i2s_runtime_suspend(&pdev->dev);
> > > > > > > > This breaks device's RPM refcounting if it was disabled in the active
> > > > > > > > state. This code should be removed. At most you could warn about the
> > > > > > > > unxpected RPM state here, but it shouldn't be necessary.
> > > > > > > I guess this was added for safety and explicit suspend keeps clock
> > > > > > > disabled.
> > > > > > > Not sure if ref-counting of the device matters when runtime PM is
> > > > > > > disabled and device is removed.
> > > > > > > I see few drivers using this way.
> > > > > > It should matter (if I'm not missing something) because RPM should
> > > > > > be in
> > > > > > a wrecked state once you'll try to re-load the driver's module. Likely
> > > > > > that those few other drivers are wrong.
> > > > > >
> > > > > > [snip]
> > > > > Once the driver is re-loaded and RPM is enabled, I don't think it
> > > > > would use
> > > > > the same 'dev' and the corresponding ref count. Doesn't it use the new
> > > > > counters?
> > > > > If RPM is not working for some reason, most likely it would be the case
> > > > > for other
> > > > > devices. What best driver can do is probably do a force suspend during
> > > > > removal if
> > > > > already not done. I would prefer to keep, since multiple drivers still
> > > > > have it,
> > > > > unless there is a real harm in doing so.
> > > > I took a closer look and looks like the counter actually should be
> > > > reset. Still I don't think that it's a good practice to make changes
> > > > underneath of RPM, it may strike back.
> > > If RPM is broken, it probably would have been caught during device usage.
> > > I will remove explicit suspend here if no any concerns from other folks.
> > > Thanks.
> > I recall that this was the preferred way of doing this from the RPM
> > folks. Tegra30 I2S driver does the same and Stephen had pointed me to
> > this as a reference.
> > I believe that this is meant to ensure that the
> > device is always powered-off regardless of it RPM is enabled or not and
> > what the current state is.
> Yes, it was kinda actual for the case of unavailable RPM.

> Anyways, /I think/ variant like this should have been more preferred:
>
> if (!pm_runtime_enabled(&pdev->dev))
>          tegra210_i2s_runtime_suspend(&pdev->dev);
> else
>          pm_runtime_disable(&pdev->dev);

I think it looks to be similar to what is there already.

pm_runtime_disable(&pdev->dev); // it would turn out to be a dummy call 
if !RPM
if (!pm_runtime_status_suspended(&pdev->dev)) // it is true always if !RPM
ÂÂÂÂÂÂÂ tegra210_i2s_runtime_suspend(&pdev->dev);
> > Now for Tegra210 (or actually 64-bit Tegra) RPM is always enabled and so
> > we don't need to worry about the !RPM case. However, I still don't see
> > the harm in this.
> There is no real harm today, but:
>
> 1. I'd prefer to be very careful with RPM in general, based on
>     previous experience.
>
> 2. It should be a bug if device isn't RPM-suspended during
>     of driver's removal. Thus the real problem needs to be fixed
>     rather than worked around.