linux-kernel - Re: [PATCH 1/2] iommu/rockchip: Handle errors returned from PM framework

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Message-ID: <3265383.PcPThIO4HC@phil>
Date:   Tue, 07 Aug 2018 15:15:39 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        Jeffy Chen <jeffy.chen@...k-chips.com>
Subject: Re: [PATCH 1/2] iommu/rockchip: Handle errors returned from PM framework

Am Dienstag, 7. August 2018, 14:31:49 CEST schrieb Marc Zyngier:
> On 07/08/18 13:09, Heiko Stuebner wrote:
> > Hi Marc,
> > 
> > Am Dienstag, 7. August 2018, 10:54:05 CEST schrieb Marc Zyngier:
> >> pm_runtime_get_if_in_use can fail: either PM has been disabled
> >> altogether (-EINVAL), or the device hasn't been enabled yet (0).
> >> Sadly, the Rockchip IOMMU driver tends to conflate the two things
> >> by considering a non-zero return value as successful.
> >>
> >> This has the consequence of hiding other bugs, so let's handle this
> >> case throughout the driver, with a WARN_ON_ONCE so that we can try
> >> and work out what happened.
> >>
> >> Fixes: 0f181d3cf7d98 ("iommu/rockchip: Add runtime PM support")
> >> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> > 
> > I'm still not sure about the !CONFIG_PM case, as it was probably silently
> > working in that case before
> 
> Do we agree that this is an orthogonal problem though?

Nope ;-) .... I.e. right now the code ignores the -EINVAL from disabled PM
and continues, possibly even handling the irq correctly.

If it actually worked is a different matter, as I guess nobody really tried
with !PM in the past.

Now with error-handling we always return IRQ_NONE for !PM.


> > But on the other hand we're also already running over it in other places
> > like in the iommu-shutdown and I guess if someone _really_ disabled
> > CONFIG_PM, a lot of additional stuff would fail anyway.
> > 
> > So should we wrap that in some #ifdef magic, just ignore it or simply
> > select PM similar to what Tegra, Renesas and Vexpress seem to do?
> > 
> > I guess I like the 3rd option best ;-)
> 
> It probably doesn't hurt. At what level do you want it? As a dependency
> to the IOMMU? or to the platform?

I guess it might be best to go the Tegra, etc way. Whoever in their right
mind would want to drive a mobile platform without any form for power
management ;-) .

I can do these patches for arm32+arm64 myself ... I just wanted to put
that thought out there - in case that was just a stupid idea of mine :-D .


Heiko