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

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Date: Tue, 28 May 2024 15:22:40 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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 Tue, May 28, 2024 at 11:21:39AM +0100, Russell King (Oracle) wrote:
> 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?

Let's drop it then, so not to cause confusion for the maintainers.

-Serge(y)

> 
> -- 
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