netdev - Re: [PATCH net-next] net: pcs: lynxi: fully reconfigure if link is down

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Message-ID: <565a8248-c4d1-f135-2499-6bbfe76def53@suse.de>
Date: Thu, 17 Aug 2023 16:13:44 +0300
From: Denis Kirjanov <dkirjanov@...e.de>
To: Daniel Golle <daniel@...rotopia.org>, Alexander Couzens <lynxis@...0.eu>,
 Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next] net: pcs: lynxi: fully reconfigure if link is
 down

On 8/17/23 15:04, Daniel Golle wrote:
> On MT7988 When switching from 10GBase-R/5GBase-R/USXGMII to one of the
> interface modes provided by mtk-pcs-lynxi we need to make sure to
> always perform a full configuration of the PHYA.
> As the idea behind not doing that was mostly to prevent an existing link
> going down without any need for it to do so. Hence we can just always
> perform a full confinguration in case the link is down.
> 
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---
>  drivers/net/pcs/pcs-mtk-lynxi.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/pcs/pcs-mtk-lynxi.c b/drivers/net/pcs/pcs-mtk-lynxi.c
> index b0f3ede945d96..788c2ccde064e 100644
> --- a/drivers/net/pcs/pcs-mtk-lynxi.c
> +++ b/drivers/net/pcs/pcs-mtk-lynxi.c
> @@ -108,8 +108,8 @@ static int mtk_pcs_lynxi_config(struct phylink_pcs *pcs, unsigned int neg_mode,
>  				bool permit_pause_to_mac)
>  {
>  	struct mtk_pcs_lynxi *mpcs = pcs_to_mtk_pcs_lynxi(pcs);
> -	bool mode_changed = false, changed;
> -	unsigned int rgc3, sgm_mode, bmcr;
> +	bool mode_changed = false, changed, link;
> +	unsigned int bm, rgc3, sgm_mode, bmcr;
>  	int advertise, link_timer;
>  
>  	advertise = phylink_mii_c22_pcs_encode_advertisement(interface,
> @@ -117,6 +117,10 @@ static int mtk_pcs_lynxi_config(struct phylink_pcs *pcs, unsigned int neg_mode,
>  	if (advertise < 0)
>  		return advertise;
>  
> +	/* Check if link is currently up */
> +	regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1, &bm);
> +	link = !!(FIELD_GET(SGMII_BMSR, bm) & BMSR_LSTATUS);
> +
>  	/* Clearing IF_MODE_BIT0 switches the PCS to BASE-X mode, and
>  	 * we assume that fixes it's speed at bitrate = line rate (in
>  	 * other words, 1000Mbps or 2500Mbps).
> @@ -137,7 +141,10 @@ static int mtk_pcs_lynxi_config(struct phylink_pcs *pcs, unsigned int neg_mode,
>  		bmcr = 0;
>  	}
>  
> -	if (mpcs->interface != interface) {
> +	/* Do a full reconfiguration only if the link is down or the interface
> +	 * mode has changed
> +	 */
> +	if (mpcs->interface != interface || !link) {

btw is it a thread-safe to check the mpcs->interface member?
I've quick checked and phylink_pcs_config can be invoked from different places
and the code below does the following assignment:
mpcs->interface = interface;

>  		link_timer = phylink_get_link_timer_ns(interface);
>  		if (link_timer < 0)
>  			return link_timer;