netdev - Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run mt7530_setup

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Date: Tue, 9 Jan 2024 16:57:40 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Arınç ÜNAL <arinc.unal@...nc9.com>
Cc: Dan Carpenter <dan.carpenter@...aro.org>,
	Simon Horman <horms@...nel.org>,
	Daniel Golle <daniel@...rotopia.org>,
	Landen Chao <Landen.Chao@...iatek.com>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	"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>,
	Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Frank Wunderlich <frank-w@...lic-files.de>,
	Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
	mithat.guner@...ont.com, erkin.bozoglu@...ont.com
Subject: Re: [PATCH net-next 07/15] net: dsa: mt7530: do not run
 mt7530_setup_port5() if port 5 is disabled

On Sat, Jan 06, 2024 at 08:01:25PM +0200, Arınç ÜNAL wrote:
> I must be missing something.
> 
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index 7f9d63b61168..05ce3face47c 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -2325,7 +2325,7 @@ mt7530_setup(struct dsa_switch *ds)
>  			if (phy_node->parent == priv->dev->of_node->parent) {
>  				ret = of_get_phy_mode(mac_np, &interface);
> -				if (ret && ret != -ENODEV) {
> +				if (ret) {
>  					of_node_put(mac_np);
>  					of_node_put(phy_node);
>  					return ret;
> 
> $ ../smatch/smatch_scripts/kchecker --spammy drivers/net/dsa/mt7530.c
>   CHECK   scripts/mod/empty.c
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   INSTALL libsubcmd_headers
>   CC      drivers/net/dsa/mt7530.o
>   CHECK   drivers/net/dsa/mt7530.c
> drivers/net/dsa/mt7530.c:469 mt7530_pad_clk_setup() error: uninitialized symbol 'ncpo1'.
> drivers/net/dsa/mt7530.c:895 mt7530_set_ageing_time() error: uninitialized symbol 'age_count'.
> drivers/net/dsa/mt7530.c:895 mt7530_set_ageing_time() error: uninitialized symbol 'age_unit'.
> drivers/net/dsa/mt7530.c:2346 mt7530_setup() error: uninitialized symbol 'interface'.

Yes, well _now_ it is a false positive, probably because smatch cannot
determine that when priv->p5_intf_sel has been set to P5_INTF_SEL_PHY_P0
or P5_INTF_SEL_PHY_P4, "interface" should have been also initialized.
But it doesn't matter, you can ignore a false positive. I'm also seeing it.
Although you should check whether treating -ENODEV as a hard error is fine
and won't cause regressions.

> Just so you know, I intend to remove this whole PHY muxing feature once I
> bring changing DSA conduit support to this subdriver. I've got two strong
> reasons for this.
> - Changing the DSA conduit achieves the same result with the only overhead
>   being the DSA header included on every frame.
> 
> - There can't be proper dt-bindings for it as the nature of the feature
>   shows that it represents an optional way to operate the hardware, it does
>   not represent a hardware design. Overall, the implementation is a hack to
>   make it work for specific hardware (switch must be connected to gmac1 of
>   a MediaTek SoC, no PHY must be present at address 0 or 4 on the MDIO bus
>   of the SoC. It should rather be configurable on userspace. Which will
>   never happen as it is specific to this switch and the changing DSA
>   conduit feature is the perfect substitute for this.

Is PHY muxing a "true" switch bypass, or is it just a route through the
switch for all packets coming from GMAC5 to go to phy0 or phy4? If the
latter, I agree that dynamic conduit changing is a more flexible option,
not to mention the user space tooling is already there.

Are there existing systems that use PHY muxing? The possible problem I
see is breaking those boards which have a phy-handle on gmac5, if the
mt7530 driver is no longer going to modify its HWTRAP register.

> 
> Let me know if you've got any suggestions that can get rid of the warning
> without reworking the whole code block. Otherwise, I'm just going to ignore
> it until I get rid of the whole code block.

The obvious way would be to leave the initialization to PHY_INTERFACE_MODE_NA
there. Or to just ignore the warning.