linux-kernel - Re: [PATCH v2 3/3] net: stmmac: Bring down the clocks to lower frequencies when mac link goes down

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Date: Wed, 26 Jun 2024 09:58:24 -0500
From: Andrew Halaney <ahalaney@...hat.com>
To: Sagar Cheluvegowda <quic_scheluve@...cinc.com>
Cc: Vinod Koul <vkoul@...nel.org>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Russell King <linux@...linux.org.uk>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Bhupesh Sharma <bhupesh.sharma@...aro.org>, kernel@...cinc.com, 
	Andrew Lunn <andrew@...n.ch>, linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/3] net: stmmac: Bring down the clocks to lower
 frequencies when mac link goes down

On Tue, Jun 25, 2024 at 04:49:30PM GMT, Sagar Cheluvegowda wrote:
> When mac link goes down we don't need to mainitain the clocks to operate
> at higher frequencies, as an optimized solution to save power when
> the link goes down we are trying to bring down the clocks to the
> frequencies corresponding to the lowest speed possible.
> 
> Signed-off-by: Sagar Cheluvegowda <quic_scheluve@...cinc.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index ec7c61ee44d4..f0166f0bc25f 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -996,6 +996,9 @@ static void stmmac_mac_link_down(struct phylink_config *config,
>  {
>  	struct stmmac_priv *priv = netdev_priv(to_net_dev(config->dev));
>  
> +	if (priv->plat->fix_mac_speed)
> +		priv->plat->fix_mac_speed(priv->plat->bsp_priv, SPEED_10, mode);
> +
>  	stmmac_mac_set(priv, priv->ioaddr, false);
>  	priv->eee_active = false;
>  	priv->tx_lpi_enabled = false;
> @@ -1004,6 +1007,11 @@ static void stmmac_mac_link_down(struct phylink_config *config,
>  
>  	if (priv->dma_cap.fpesel)
>  		stmmac_fpe_link_state_handle(priv, false);
> +
> +	stmmac_set_icc_bw(priv, SPEED_10);
> +
> +	if (priv->plat->fix_mac_speed)
> +		priv->plat->fix_mac_speed(priv->plat->bsp_priv, SPEED_10, mode);


I think you're doing this at the beginning and end of
stmmac_mac_link_down(), is that intentional?

I'm still curious if any of the netdev folks have any opinion on scaling
things down like this on link down.