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

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Date:   Tue, 7 Aug 2018 15:25:53 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Heiko Stuebner <heiko@...ech.de>
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

On 07/08/18 14:15, Heiko Stuebner wrote:
> 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.

Ah, I now see what you mean. Yeah, this is a bit rubbish. It would have
been better if the API returned something more sensible in that case,
but that's a bit late...

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

I don't think anyone noticed. !CONFIG_PM on something like rk3399
probably isn't very popular, and certainly comes for free on a
multiplatform kernel.

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

Yup.

>>> 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 .

Not stupid at all. Regarding this very patch: where do you want me to
take it?

	M.
-- 
Jazz is not dead. It just smells funny...