linux-kernel - Re: [PATCH net-next v2 4/5] net: ravb: Do not apply RX checksum settings to hardware if the interface is down

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Date: Sun, 11 Feb 2024 12:13:18 +0000
From: Biju Das <biju.das.au@...il.com>
To: Sergei Shtylyov <sergei.shtylyov@...il.com>
Cc: Sergey Shtylyov <s.shtylyov@....ru>, Biju Das <biju.das.jz@...renesas.com>, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, claudiu.beznea@...on.dev, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org, 
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 4/5] net: ravb: Do not apply RX checksum
 settings to hardware if the interface is down

Hi Sergey,

On Sun, Feb 11, 2024 at 9:40 AM Sergei Shtylyov
<sergei.shtylyov@...il.com> wrote:
>
> On 2/11/24 11:56 AM, Biju Das wrote:
>
> >>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> >>>>
> >>>> Do not apply the RX checksum settings to hardware if the interface is
> >>>> down.
> >>>> In case runtime PM is enabled, and while the interface is down, the IP
> >>>> will be in reset mode (as for some platforms disabling the clocks will
> >>>> switch the IP to reset mode, which will lead to losing register
> >>>> contents) and applying settings in reset mode is not an option.
> >>>> Instead, cache the RX checksum settings and apply them in ravb_open()
> >>>> through ravb_emac_init().
> >>>> This has been solved by introducing pm_runtime_active() check. The
> >>>> device runtime PM usage counter has been incremented to avoid
> >>>> disabling the device clocks while the check is in progress (if any).
> >>>>
> >>>> Commit prepares for the addition of runtime PM.
> >>>>
> >>>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> >>>
> >>> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
> >>
> >> This will do the same job, without code duplication right?
> >>
> >>> static int ravb_set_features(struct net_device *ndev,
> >>>     netdev_features_t features)
> >>> {
> >>> struct ravb_private *priv = netdev_priv(ndev);
> >>> struct device *dev = &priv->pdev->dev;
> >>> const struct ravb_hw_info *info = priv->info;
> >>>
> >>> pm_runtime_get_noresume(dev);
> >>> if (!pm_runtime_active(dev)) {
> >>> pm_runtime_put_noidle(dev);
> >>> ndev->features = features;
> >>> return 0;
> >>> }
> >>>
> >>> return info->set_feature(ndev, features);
> >
> >> We now leak the device reference by not calling pm_runtime_put_noidle()
> >> after this statement...
> >
> > Oops. So this leak  can be fixed like [1]
> >
> >>  The approach seems sane though -- Claudiu, please consider following it.
> >
> > [1]
> > static int ravb_set_features(struct net_device *ndev,
> >     netdev_features_t features)
> > {
> > struct ravb_private *priv = netdev_priv(ndev);
> > const struct ravb_hw_info *info = priv->info;
> > struct device *dev = &priv->pdev->dev;
> > bool pm_active;
> >
> > pm_runtime_get_noresume(dev);
> > pm_active = pm_runtime_active(dev);
> > pm_runtime_put_noidle(dev);
>
>    There is no point dropping the RPM reference before we access
> the regs...

I don't think there is an issue in accessing register by the usage of
below API's

pm_runtime_get_noresume:--- Bump up runtime PM usage counter of a device.
pm_runtime_active:--- Check whether or not a device is runtime-active.
pm_runtime_put_noidle:--Drop runtime PM usage counter of a device.

Cheers,
Biju