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

[Sagar Cheluvegowda <quic_scheluve@quicinc.com>]

On 6/28/2024 3:16 PM, Russell King (Oracle) wrote:
> On Tue, Jun 25, 2024 at 04:49:30PM -0700, 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.
> 
> I thought I had already commented on a similar patch, but I can't find
> anything in my mailboxes to suggest I had.
> 
>> 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);
> 
> Two things here:
> 
> 1) Why do we need to call fix_mac_speed() at the start and end of this
>    stmmac_mac_link_down()?
This was a typo, i will remove this.
> 
> 2) What if the MAC doesn't support 10M operation? For example, dwxgmac2
>    and dwxlgmac2 do not support anything below 1G. It feels that this
>    is storing up a problem for the future, where a platform that uses
>    e.g. xlgmac2 also implements fix_mac_speed() and then gets a
>    surprise when it's called with SPEED_10.
> 
> Personally, I don't like "fix_mac_speed", and I don't like it even more
> with this change. I would prefer to see link_up/link_down style
> operations so that platforms can do whatever they need to on those
> events, rather than being told what to do by a single call that may
> look identical irrespective of whether the link came up or went down.
> 
I will drop this patch[3/3] from this series now and i will do some analysis
on platform level link up and link down functions and post the changes as a
new series altogether.