linux-kernel - Re: [PATCH 1/3] net: stmmac: dwmac-rk: Use DELAY

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Message-ID: <f5f397bb-476a-429a-9d1e-1c1a9beb8f89@lunn.ch>
Date: Fri, 7 Mar 2025 14:52:13 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jonas Karlman <jonas@...boo.se>
Cc: Heiko Stuebner <heiko@...ech.de>, Andrew Lunn <andrew+netdev@...n.ch>,
	"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>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Wadim Egorov <w.egorov@...tec.de>, netdev@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 1/3] net: stmmac: dwmac-rk: Use DELAY_ENABLE macro for
 RK3328

On Fri, Mar 07, 2025 at 12:28:42AM +0100, Jonas Karlman wrote:
> Hi Andrew,
> 
> On 2025-03-06 23:25, Andrew Lunn wrote:
> > On Thu, Mar 06, 2025 at 08:38:52PM +0000, Jonas Karlman wrote:
> >> Support for Rockchip RK3328 GMAC and addition of the DELAY_ENABLE macro
> >> was merged in the same merge window. This resulted in RK3328 not being
> >> converted to use the new DELAY_ENABLE macro.
> >>
> >> Change to use the DELAY_ENABLE macro to help disable MAC delay when
> >> RGMII_ID/RXID/TXID is used.
> >>
> >> Fixes: eaf70ad14cbb ("net: stmmac: dwmac-rk: Add handling for RGMII_ID/RXID/TXID")
> > 
> > Please add a description of the broken behaviour. How would i know i
> > need this fix? What would i see?
> 
> Based on my layman testing I have not seen any real broken behaviour
> with current enablement of a zero rx/tx MAC delay for RGMII_ID/RXID/TXID.
> 
> The driver ops is called with a rx/tx_delay=0 for RGMII_ID/RXID/TXID
> modes, what the MAC does with enable=true and rx/tx_delay=0 is unclear
> to me.
> 
> > 
> > We also need to be careful with backwards compatibility. Is there the
> > potential for double bugs cancelling each other out? A board which has
> > the wrong phy-mode in DT, but because of this bug, the wrong register
> > is written and it actually works because of reset defaults?
> 
> To my knowledge this should have very limited effect, however I am no
> network expert and after doing very basic testing on several different
> rk3328/rk3566/rk3568/rk3588 I could not see any real affect with/without
> this change.
> 
> The use of Fixes-tag was more to have a reference to the commit that
> first should have used the DELAY_ENABLE macro.

https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

  It must either fix a real bug that bothers people or just add a device ID.

It does not sound like this meets the stable requirements. Plus there
is the potential for breakage. So i suggest you drop the Fixes: tag
and we merge this via net-next.

Please take a look at:

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html

    Andrew

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