linux-kernel - Re: [PATCH 3/4] memory: mtk-smi: Add sleep ctrl function

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Message-ID: <e1d72db69f424b9ee8987b7bafa7423c672ceef1.camel@mediatek.com>
Date:   Tue, 7 Dec 2021 20:10:08 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
CC:     Krzysztof Kozlowski <krzk@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Tomasz Figa" <tfiga@...omium.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>, <youlin.pei@...iatek.com>,
        <anan.sun@...iatek.com>, <lc.kan@...iatek.com>,
        <yi.kuo@...iatek.com>, <anthony.huang@...iatek.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>
Subject: Re: [PATCH 3/4] memory: mtk-smi: Add sleep ctrl function

On Tue, 2021-12-07 at 09:56 +0100, AngeloGioacchino Del Regno wrote:
> Il 07/12/21 07:24, Yong Wu ha scritto:
> > Hi AngeloGioacchino,
> > 
> > Thanks for your review.
> > 
> > On Mon, 2021-12-06 at 16:08 +0100, AngeloGioacchino Del Regno
> > wrote:
> > > Il 03/12/21 07:40, Yong Wu ha scritto:
> > > > sleep control means that when the larb go to sleep, we should
> > > > wait
> > > > a bit
> > > > until all the current commands are finished. thus, when the
> > > > larb
> > > > runtime
> > > > suspend, we need enable this function to wait until all the
> > > > existed
> > > > command are finished. when the larb resume, just disable this
> > > > function.
> > > > This function only improve the safe of bus. Add a new flag for
> > > > this
> > > > function. Prepare for mt8186.
> > > > 
> > > > Signed-off-by: Anan Sun <anan.sun@...iatek.com>
> > > > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > > > ---
> > > >    drivers/memory/mtk-smi.c | 39
> > > > +++++++++++++++++++++++++++++++++++----
> > > >    1 file changed, 35 insertions(+), 4 deletions(-)
> > 
> > [snip]
> > 
> > > >    static int __maybe_unused mtk_smi_larb_suspend(struct device
> > > > *dev)
> > > >    {
> > > >    	struct mtk_smi_larb *larb = dev_get_drvdata(dev);
> > > > +	int ret = 0;
> > > > +
> > > > +	if (MTK_SMI_CAPS(larb->larb_gen->flags_general,
> > > > MTK_SMI_FLAG_SLEEP_CTL))
> > > > +		ret = mtk_smi_larb_sleep_ctrl(dev, true);
> > > 
> > > Sorry but what happens if SLP_PROT_RDY is not getting set
> > > properly?
> > >   From what I can understand in the commit description that you
> > > wrote,
> > > if we reach
> > > the timeout, then the LARB transactions are not over....
> > > 
> > > I see that you are indeed returning a failure here, but you are
> > > also
> > > turning off
> > > the clocks regardless of whether we get a failure or a success;
> > > I'm
> > > not sure that
> > > this is right, as this may leave the hardware in an unpredictable
> > > state (since
> > > there were some more LARB transactions that didn't go through),
> > > leading to crashes
> > > at system resume (or when retyring to suspend).
> > 
> > Thanks for this question. In theory you are right. In this case,
> > the
> > bus already hang.
> > 
> > We only printed a fail log in this patch. If this fail happens, we
> > should request the master to check which case cause the larb hang.
> > 
> > If the master has a good reason or limitation, the hang is
> > expected, I
> > think we have to add larb reset in this fail case: Reset the larb
> > when
> > the larb runtime resume.
> > 
> 
> Think about the case in which the system gets resumed only partially
> due to a
> 
> failure during resume of some driver, or due to a RTC or arch timer
> resume and
> suspend right after... or perhaps during runtime suspend/resume of
> some devices.
> In that case, we definitely want to avoid any kind of failure point
> that would
> lead to a system crash, or any kind of user noticeable (or UX
> disrupting) "strange
> behavior".
> 
> I think that we should make sure that the system suspends cleanly,
> instead of
> patching up any possible leftover issue at resume time: if this is
> doable with
> a LARB reset in suspend error case, that looks like being a good
> option indeed.
> 
> As a side note, thinking about UX, losing a little more time during
> suspend is
> nothing really noticeable for the user... on the other hand, spending
> more time
> during resume may be something noticeable to the user.
> For this reason, I think that guaranteeing that the system resumes as
> fast as
> possible is very important, which adds up to the need of suspending
> cleanly.

Thanks for this comment. I will put it in the suspend when adding the
reset. But I have no plan to add it in this version since I don't see
the need for this right now. Maybe I should add a comment in the code
for this.

> 
> > Fortunately, we have never got this issue. We could add this reset
> > when
> > necessary. Is this OK for you?
> > 
> > Thanks.
> > 
> > > 
> > > >    
> > > >    	clk_bulk_disable_unprepare(larb->smi.clk_num, larb-
> > > > >smi.clks);
> > > > -	return 0;
> > > > +	return ret;
> > > >    }
> > > >    
> > > >    static const struct dev_pm_ops smi_larb_pm_ops = {
> > > > 
> > > 
> > > 
> 
>