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

[AngeloGioacchino Del Regno]

Il 07/12/21 13:10, Yong Wu ha scritto:
> 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@xxxxxxxxxxxx>
> > > > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > > > > ---
> > > > >     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.

What I understand from your reply is that the reset is not trivial work
and needs quite some time to be done properly; in that case: yes, please
add a TODO comment that explains the situation and the discussed solution.

Also, since this SLP_PROT_RDY flag seems to be very nice, just a simple
question: is this a new feature in the SMI IP of MT8186, or is there anything
similar that we may use on other SoCs, like 8183, 8192, 8195, as a follow-up
of this series?

> > > 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 = {