linux-kernel - Re: [PATCH] net: stmmac: disable/enable ptp_ref

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Message-ID: <1570782069.5044.12.camel@mhfsdcap03>
Date:   Fri, 11 Oct 2019 16:21:09 +0800
From:   biao huang <biao.huang@...iatek.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     <davem@...emloft.net>, Jose Abreu <joabreu@...opsys.com>,
        <andrew@...n.ch>, Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <netdev@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <yt.shen@...iatek.com>,
        <jianguo.zhang@...iatek.com>, <boon.leong.ong@...el.com>,
        <yong.wu@...iatek.com>
Subject: Re: [PATCH] net: stmmac: disable/enable ptp_ref_clk in
 suspend/resume flow

Appreciate your comments!

On Thu, 2019-10-10 at 16:01 -0700, Jakub Kicinski wrote:
> On Wed, 9 Oct 2019 16:56:49 +0800, Biao Huang wrote:
> > disable ptp_ref_clk in suspend flow, and enable it in resume flow.
> > 
> > Signed-off-by: Biao Huang <biao.huang@...iatek.com>
> > ---
> >  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index c7c9e5f162e6..b592aeecc3dd 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -4469,6 +4469,8 @@ int stmmac_suspend(struct device *dev)
> >  		stmmac_mac_set(priv, priv->ioaddr, false);
> >  		pinctrl_pm_select_sleep_state(priv->device);
> >  		/* Disable clock in case of PWM is off */
> > +		if (priv->plat->clk_ptp_ref)
> > +			clk_disable_unprepare(priv->plat->clk_ptp_ref);
> 
> I don't know much embedded, but it seems like this should perhaps just
> be clk_disable() without the unprepare? stmmac_hw_teardown() is called
> when driver is removed so it needs to unprepare as well.
> 
> Please feel free to explain to me why this needs to be
> clk_disable_unprepare(), as I said - not an expert.
> 
As our clock owner's advice, there are prepare/unprepare clk_ops for
pll, but no enable/disable clk_ops for it, and pll will be off only when
the prepare reference count decrease to 0.

so for the sake of power saving, we'd better call clk_disable_unprepare
to turn the parent pll off.

> Also - if this is a bug fix and you'd like to have it backported to
> older releases you need to add a Fixes tag.
> 
Thanks for the reminder, I'll add the fixes tag in the next version.
> Thanks!
> 
> >  		clk_disable(priv->plat->pclk);
> >  		clk_disable(priv->plat->stmmac_clk);
maybe it should be clk_disable_unprepare(priv->plat->pclk);
		   clk_disable_unprepare(priv->plat->stmmac_clk);
> >  	}
> > @@ -4535,6 +4537,8 @@ int stmmac_resume(struct device *dev)
> >  		/* enable the clk previously disabled */
> >  		clk_enable(priv->plat->stmmac_clk);
> >  		clk_enable(priv->plat->pclk);
> > +		if (priv->plat->clk_ptp_ref)
> > +			clk_prepare_enable(priv->plat->clk_ptp_ref);
> >  		/* reset the phy so that it's ready */
> >  		if (priv->mii)
> >  			stmmac_mdio_reset(priv->mii);
>