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From:   Jassi Brar <jassisinghbrar@gmail.com>
Date:   Sat, 30 May 2020 15:43:20 -0500
Message-ID: <CABb+yY2J5Q6uvXNk0KE3QL32C_J3RFHJJX_tq4R9arAcvJ262g@mail.gmail.com>
Subject: Re: [PATCH] mailbox: imx: Add context save/restore for suspend/resume
To:     Anson Huang <anson.huang@nxp.com>
Cc:     Aisheng Dong <aisheng.dong@nxp.com>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        dl-linux-imx <linux-imx@nxp.com>
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On Wed, May 27, 2020 at 8:55 PM Anson Huang <anson.huang@nxp.com> wrote:
>
> Gentle ping...
>
>
> > Subject: RE: [PATCH] mailbox: imx: Add context save/restore for
> > suspend/resume
> >
> >
> >
> > > Subject: RE: [PATCH] mailbox: imx: Add context save/restore for
> > > suspend/resume
> > >
> > > > From: Anson Huang <anson.huang@nxp.com>
> > > > Sent: Friday, April 24, 2020 10:33 AM
> > > >
> > > > > Subject: RE: [PATCH] mailbox: imx: Add context save/restore for
> > > > > suspend/resume
> > > > >
> > > > > > From: Anson Huang <Anson.Huang@nxp.com>
> > > > > > Sent: Friday, April 24, 2020 7:01 AM
> > > > > >
> > > > > > For "mem" mode suspend on i.MX8 SoCs, MU settings could be lost
> > > > > > because its power is off, so save/restore is needed for MU
> > > > > > settings during
> > > > > suspend/resume.
> > > > > > However, the restore can ONLY be done when MU settings are
> > > > > > actually lost, for the scenario of settings NOT lost in "freeze"
> > > > > > mode suspend, since there could be still IPC going on multiple
> > > > > > CPUs, restoring the MU settings could overwrite the TIE by
> > > > > > mistake and cause system freeze, so need to make sure ONLY
> > > > > > restore the MU settings when it is
> > > > > powered off.
> > > > > >
> > > > > > Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
> > > > >
> > > > > As mentioned before, we'd better keep the original author.
> > > > >
> > > > > > ---
> > > > > >  drivers/mailbox/imx-mailbox.c | 35
> > > > > > +++++++++++++++++++++++++++++++++++
> > > > > >  1 file changed, 35 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/mailbox/imx-mailbox.c
> > > > > > b/drivers/mailbox/imx-mailbox.c index 97bf0ac..b53cf63 100644
> > > > > > --- a/drivers/mailbox/imx-mailbox.c
> > > > > > +++ b/drivers/mailbox/imx-mailbox.c
> > > > > > @@ -67,6 +67,8 @@ struct imx_mu_priv {
> > > > > >       struct clk              *clk;
> > > > > >       int                     irq;
> > > > > >
> > > > > > +     u32 xcr;
> > > > > > +
> > > > > >       bool                    side_b;
> > > > > >  };
> > > > > >
> > > > > > @@ -583,12 +585,45 @@ static const struct of_device_id
> > > > > > imx_mu_dt_ids[] = {  };  MODULE_DEVICE_TABLE(of, imx_mu_dt_ids);
> > > > > >
> > > > > > +static int imx_mu_suspend_noirq(struct device *dev) {
> > > > > > +     struct imx_mu_priv *priv = dev_get_drvdata(dev);
> > > > > > +
> > > > > > +     priv->xcr = imx_mu_read(priv, priv->dcfg->xCR);
> > > > > > +
> > > > > > +     return 0;
> > > > > > +}
> > > > > > +
> > > > > > +static int imx_mu_resume_noirq(struct device *dev) {
> > > > > > +     struct imx_mu_priv *priv = dev_get_drvdata(dev);
> > > > > > +
> > > > > > +     /*
> > > > > > +      * ONLY restore MU when context lost, the TIE could
> > > > > > +      * be set during noirq resume as there is MU data
> > > > > > +      * communication going on, and restore the saved
> > > > > > +      * value will overwrite the TIE and cause MU data
> > > > > > +      * send failed, may lead to system freeze. This issue
> > > > > > +      * is observed by testing freeze mode suspend.
> > > > > > +      */
> > > > > > +     if (!imx_mu_read(priv, priv->dcfg->xCR))
> > > > > > +             imx_mu_write(priv, priv->xcr, priv->dcfg->xCR);
> > > > >
> > > > > This could be separate patch if it aims to fix a specific corner case.
> > > >
> > > > This is NOT corner case, it can be reproduced with our imx_5.4.y
> > > > very easily, and this issue cause me many days to debug...Also cause
> > > > Clark's effort to help test it a lot for many days...
> > > >
> > >
> > > Is this issue only happen for non-state lost case (eg. Freeze mode)?
> > > If yes, it's a specific case and worth a separate patch to highlight it IMHO.
> > >
> > > BTW, it seems most drivers have this issue in current kernel because
> > > they don't know whether the state are really lost, it seems like
> > > kernel still doesn't support this well.
> > >
> > > > I do NOT think it makes sense to first send out your patch with bug
> > > > for review, And then add another patch to fix it. 1 patch is enough
> > > > for this
> > > feature.
> > > >
> > >
> > > Anyway, if you really want to go with one patch, for this case, we
> > > usually could keep original author and add a small fix note in commit
> > message.
> > > (You could see many community guys do like this if you search kernel
> > > commit
> > > log)
> > >
> > > Basically we try our best to keep origin author in order to respect
> > > others' work for community work.
> >
> > I am fine with whoever is the author, my focus is the issue fix and easy rebase.
> > If maintainer agrees that introduce a patch with bug and add another patch to
> > fix is OK, then I can rework the patch into 2 patches.
> >
Not two patches, just add to the original patch and add a fix note in
commit as Anson suggested ... though I don't know what the original
patch was. But I am definitely in support of giving credit to the
original author.

thanks.