linux-kernel - Re: [PATCH v6 3/3] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module

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Message-ID: <CALAqxLVDm923WRSB+DVxFacmEtmEPS7Qeq+rW_jbCDMNMWw9PQ@mail.gmail.com>
Date:   Mon, 16 Nov 2020 11:48:39 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Will Deacon <will@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Maulik Shah <mkshah@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Hunter <jonathanh@...dia.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v6 3/3] firmware: QCOM_SCM: Allow qcom_scm driver to be
 loadable as a permenent module

On Mon, Nov 16, 2020 at 8:36 AM Will Deacon <will@...nel.org> wrote:
> On Mon, Nov 16, 2020 at 04:59:36PM +0100, Thierry Reding wrote:
> > On Fri, Nov 06, 2020 at 04:27:10AM +0000, John Stultz wrote:
> > Unfortunately, the ARM SMMU module will eventually end up being loaded
> > once the root filesystem has been mounted (for example via SDHCI or
> > Ethernet, both with using just plain, non-IOMMU-backed DMA API) and then
> > initialize, configuring as "fault by default", which then results from a
> > slew of SMMU faults from all the devices that have previously configured
> > themselves without IOMMU support.
>
> I wonder if fw_devlink=on would help here?
>
> But either way, I'd be more inclined to revert this change if it's causing
> problems for !QCOM devices.
>
> Linus -- please can you drop this one (patch 3/3) for now, given that it's
> causing problems?

Agreed. Apologies again for the trouble.

I do feel like the probe timeout to handle optional links is causing a
lot of the trouble here. I expect fw_devlink would solve this, but it
may be awhile before it can be always enabled.  I may see about
pushing the default probe timeout value to be a little further out
than init (I backed away from my last attempt as I didn't want to
cause long (30 second) delays for cases like NFS root, but maybe 2-5
seconds would be enough to make things work better for everyone).

thanks
-john