linux-kernel - RE: [PATCH] mailbox: imx: Add context save/restore for suspend/resume

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Message-ID: <DB3PR0402MB39164CB0791AB259CE62EC4EF5D00@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Fri, 24 Apr 2020 03:09:25 +0000
From:   Anson Huang <anson.huang@....com>
To:     Aisheng Dong <aisheng.dong@....com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     dl-linux-imx <linux-imx@....com>
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@....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@....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@....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.

Anson