linux-kernel - Re: [PATCH RFC net-next 2/3] net: stmmac: Activate Inband/PCS flag based on the selected iface

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Message-ID: <ZlWwMzMZrwb5fscN@shell.armlinux.org.uk>
Date: Tue, 28 May 2024 11:21:39 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"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>,
	Byungho An <bh74.an@...sung.com>,
	Giuseppe CAVALLARO <peppe.cavallaro@...com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net-next 2/3] net: stmmac: Activate Inband/PCS flag
 based on the selected iface

On Mon, May 27, 2024 at 12:57:02AM +0300, Serge Semin wrote:
> On Sun, May 26, 2024 at 05:49:48PM +0100, Russell King (Oracle) wrote:
> > On Sat, May 25, 2024 at 12:02:58AM +0300, Serge Semin wrote:
> > > The HWFEATURE.PCSSEL flag is set if the PCS block has been synthesized
> > > into the DW GMAC controller. It's always done if the controller supports
> > > at least one of the SGMII, TBI, RTBI PHY interfaces. If none of these
> > > interfaces support was activated during the IP-core synthesize the PCS
> > > block won't be activated either and the HWFEATURE.PCSSEL flag won't be
> > > set. Based on that the RGMII in-band status detection procedure
> > > implemented in the driver hasn't been working for the devices with the
> > > RGMII interface support and with none of the SGMII, TBI, RTBI PHY
> > > interfaces available in the device.
> > > 
> > > Fix that just by dropping the dma_cap.pcs flag check from the conditional
> > > statement responsible for the In-band/PCS functionality activation. If the
> > > RGMII interface is supported by the device then the in-band link status
> > > detection will be also supported automatically (it's always embedded into
> > > the RGMII RTL code). If the SGMII interface is supported by the device
> > > then the PCS block will be supported too (it's unconditionally synthesized
> > > into the controller). The later is also correct for the TBI/RTBI PHY
> > > interfaces.
> > > 
> > > Note while at it drop the netdev_dbg() calls since at the moment of the
> > > stmmac_check_pcs_mode() invocation the network device isn't registered. So
> > > the debug prints will be for the unknown/NULL device.
> > 
> 
> > Thanks. As this is a fix, shouldn't it be submitted for the net tree as
> > it seems to be fixing a bug in the driver as it stands today?
> 
> From one point of view it could be submitted for the net tree indeed,
> but on the second thought are you sure we should be doing that seeing
> it will activate the RGMII-inband detection and the code with the
> netif-carrier toggling behind the phylink back? Who knows what new
> regressions the activated PCS-code can cause?..

If it's not a fix that is suitable without the remainder of the patch
set, this should be stated in the commit description and it shouldn't
have a Fixes: tag.

The reason is because it wouldn't be stable kernel material without the
other patches - if stable picks it up without the other patches then
it could end up being applied without the other patches resulting in
the situation you mention above.

Shall I remove the Fixes: tag?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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