From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH 1/2] iommu/rockchip: Handle errors returned from PM framework Date: Tue, 7 Aug 2018 15:25:53 +0100 Message-ID: <5aa8d184-0c58-3471-a661-8a66a93271c7@arm.com> References: <20180807085406.3863-1-marc.zyngier@arm.com> <2940317.dDZy1L4CDY@phil> <94b6aab1-e8d3-6929-a2e6-2f06c564bc70@arm.com> <3265383.PcPThIO4HC@phil> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <3265383.PcPThIO4HC@phil> Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org To: Heiko Stuebner Cc: linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Joerg Roedel , Jeffy Chen List-Id: linux-rockchip.vger.kernel.org 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 >>> >>> 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...