netdev - Re: [PATCH net-next] net: stmmac: allow ethtool action on PCI devices if device is down

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Date:   Fri, 31 Mar 2023 12:48:43 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Corinna Vinschen <vinschen@...hat.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: stmmac: allow ethtool action on PCI devices
 if device is down

On 31.03.2023 11:23, Corinna Vinschen wrote:
> So far stmmac is only able to handle ethtool commands if the device
> is UP.  However, PCI devices usually just have to be in the active
> state for ethtool commands.
> 
What do mean with "active state" here? D0? Or, as you say "connected
to PCI" a few lines later, do you refer to hot-plugging?

PCI being in D0 often isn't sufficient, especially if interface is down.
Then required resources like clocks may be disabled by the driver.

A driver may runtime-suspend a device for multiple reasons, e.g.
interface down or link down. Then the device may be put to D3hot
to save power.
If we say that it's worth to wake a device for an ethtool command,
then I wonder whether this is something that should be done in net
core. E.g. calling pm_runtime_get_sync() in __dev_ethtool, similar to
what we do in __dev_open() to deal with run-time suspended and
therefore potentially detached devices.

> Rename stmmac_check_if_running to stmmac_ethtool_begin and add a
> stmmac_ethtool_complete action.  Check if the device is connected
> to PCI and if so, just make sure the device is active.  Reset it
> to idle state as complete action.
> 
> Tested on Intel Elkhart Lake system.
> 
> Signed-off-by: Corinna Vinschen <vinschen@...hat.com>
> ---
>  .../ethernet/stmicro/stmmac/stmmac_ethtool.c  | 20 +++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> index 35c8dd92d369..5a57970dc06a 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c
> @@ -14,6 +14,7 @@
>  #include <linux/mii.h>
>  #include <linux/phylink.h>
>  #include <linux/net_tstamp.h>
> +#include <linux/pm_runtime.h>
>  #include <asm/io.h>
>  
>  #include "stmmac.h"
> @@ -429,13 +430,27 @@ static void stmmac_ethtool_setmsglevel(struct net_device *dev, u32 level)
>  
>  }
>  
> -static int stmmac_check_if_running(struct net_device *dev)
> +static int stmmac_ethtool_begin(struct net_device *dev)
>  {
> +	struct stmmac_priv *priv = netdev_priv(dev);
> +
> +	if (priv->plat->pdev) {
> +		pm_runtime_get_sync(&priv->plat->pdev->dev);
> +		return 0;
> +	}
>  	if (!netif_running(dev))
>  		return -EBUSY;
>  	return 0;
>  }
>  
> +static void stmmac_ethtool_complete(struct net_device *dev)
> +{
> +	struct stmmac_priv *priv = netdev_priv(dev);
> +
> +	if (priv->plat->pdev)
> +		pm_runtime_put(&priv->plat->pdev->dev);
> +}
> +
>  static int stmmac_ethtool_get_regs_len(struct net_device *dev)
>  {
>  	struct stmmac_priv *priv = netdev_priv(dev);
> @@ -1152,7 +1167,8 @@ static int stmmac_set_tunable(struct net_device *dev,
>  static const struct ethtool_ops stmmac_ethtool_ops = {
>  	.supported_coalesce_params = ETHTOOL_COALESCE_USECS |
>  				     ETHTOOL_COALESCE_MAX_FRAMES,
> -	.begin = stmmac_check_if_running,
> +	.begin = stmmac_ethtool_begin,
> +	.complete = stmmac_ethtool_complete,
>  	.get_drvinfo = stmmac_ethtool_getdrvinfo,
>  	.get_msglevel = stmmac_ethtool_getmsglevel,
>  	.set_msglevel = stmmac_ethtool_setmsglevel,