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 12:40:01 +0300
From: Sergei Shtylyov <sergei.shtylyov@...il.com>
To: Biju Das <biju.das.au@...il.com>, Sergey Shtylyov <s.shtylyov@....ru>
Cc: 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

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...

> if (pm_active )
>      return info->set_feature(ndev, features);

   As I said, we should call pm_runtime_put_noidle() here...
 
> ndev->features = features;
> return 0;
> }

MBR, Sergey