Re: [PATCH net 5/5] net: pcs: rzn1-miic: Init RX clock early if MAC requires it

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Romain Gantois <romain.gantois@bootlin.com>
Cc: "Alexandre Torgue" <alexandre.torgue@foss.st.com>,
	"Jose Abreu" <joabreu@synopsys.com>,
	"Andrew Lunn" <andrew@lunn.ch>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
	"Clément Léger" <clement.leger@bootlin.com>,
	"Marek Vasut" <marex@denx.de>,
	"Clark Wang" <xiaoning.wang@nxp.com>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Sylvain Girard" <sylvain.girard@se.com>,
	"Pascal EBERHARD" <pascal.eberhard@se.com>,
	netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH net 5/5] net: pcs: rzn1-miic: Init RX clock early if MAC requires it
Date: Wed, 3 Jan 2024 15:01:07 +0000	[thread overview]
Message-ID: <ZZV2s/TGKanl76TI@shell.armlinux.org.uk> (raw)
In-Reply-To: <20240103142827.168321-6-romain.gantois@bootlin.com>

On Wed, Jan 03, 2024 at 03:28:25PM +0100, Romain Gantois wrote:
> The GMAC1 controller in the RZN1 IP requires the RX MII clock signal to be
> started before it initializes its own hardware, thus before it calls
> phylink_start.
> 
> Check the rxc_always_on pcs flag and enable the clock signal during the
> link validation phase.

However, validation is *not* supposed to change the configuration of
the hardware. Validation may fail. The "interface" that gets passed
to validation may never ever be selected. This change feels like
nothing more than a hack.

Since the MAC driver has to itself provide the PCS to phylink via the
mac_select_pcs() method, the MAC driver already has knowledge of which
PCS it is going to be using. Therefore, I think it may make sense
to do something like this:

int phylink_pcs_preconfig(struct phylink *pl, struct phylink_pcs *pcs)
{
	if (pl->config->mac_requires_rxc)
		pcs->rxc_always_on = true;

	if (pcs->ops->preconfig)
		pcs->ops->pcs_preconfig(pcs);
}

and have stmmac call phylink_pcs_preconfig() for each PCS that it will
be using during initialisation / resume paths?

-- 
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