linux-kernel - Re: [PATCH RFC net-next v2 17/17] net: stmmac: pcs: Drop the

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Message-ID: <tqghwucifrtbeeucsrbbc4zx22axaij7f4qx3rwhj27kmohgci@zin7ke5272n5>
Date: Thu, 4 Jul 2024 16:19:47 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Halaney <ahalaney@...hat.com>, 
	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>, Alexei Starovoitov <ast@...nel.org>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Daniel Borkmann <daniel@...earbox.net>, linux-arm-kernel@...ts.infradead.org, 
	linux-stm32@...md-mailman.stormreply.com, bpf@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC net-next v2 17/17] net: stmmac: pcs: Drop the _SHIFT
 macros

On Fri, Jun 28, 2024 at 03:42:41PM +0100, Russell King (Oracle) wrote:
> On Mon, Jun 24, 2024 at 04:26:34PM +0300, Serge Semin wrote:
> > The PCS_ANE_PSE_SHIFT and PCS_ANE_RFE_SHIFT are unused anyway. Moreover
> > PCS_ANE_PSE and PCS_ANE_RFE are the respective field masks. So the
> > FIELD_GET()/FIELD_SET() macro-functions can be used to get/set the fields
> > content. Drop the _SHIFT macros for good then.
> > 
> > Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> > ---
> >  drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.h | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.h b/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.h
> > index a17e5b37c411..0f15c9898788 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.h
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_pcs.h
> > @@ -43,9 +43,7 @@
> >  #define PCS_ANE_FD		BIT(5)		/* AN Full-duplex flag */
> >  #define PCS_ANE_HD		BIT(6)		/* AN Half-duplex flag */
> >  #define PCS_ANE_PSE		GENMASK(8, 7)	/* AN Pause Encoding */
> > -#define PCS_ANE_PSE_SHIFT	7
> >  #define PCS_ANE_RFE		GENMASK(13, 12)	/* AN Remote Fault Encoding */
> > -#define PCS_ANE_RFE_SHIFT	12
> >  #define PCS_ANE_ACK		BIT(14)		/* AN Base-page acknowledge */
> 

> I would actually like to see all these go away.
> 
> PCS_ANE_FD == LPA_1000XFULL
> PCS_ANE_HD == LPA_1000XHALF
> PCS_ANE_PSE == LPA_1000XPAUSE and LPA_1000XPAUSE_ASYM
> PCS_ANE_RFE == LPA_RESV and LPA_RFAULT
> PCS_ANE_ACK == LPA_LPACK

Great! It will be even better.

> 
> Isn't it rather weird that the field layout matches 802.3z aka
> 1000base-X and not SGMII? This layout would not make sense for Cisco
> SGMII as it loses the speed information conveyed by the Cisco SGMII
> control word.
> 
> This isn't a case of the manufacturer using "SGMII" to mean a serial
> gigabit media independent interface that supports 1000base-X
> (PHY_INTERFACE_MODE_1000BASEX) rather than Cisco SGMII
> (PHY_INTERFACE_MODE_SGMII) ?

It's not that weird. The only CSRs available and functional for SGMII
PCS are PCS_AN_CTRL and PCS_AN_STATUS (plus PCS_SRGMII_CSR where the
PCS exposes the link status, aka Cisco SGMII tx_config_reg[15:0] with
the vendor-specific layout). Registers from PCS_ANE_ADV up to PCS_TBI_EXT
exist for TBI and RTBI PCS only. Since TBI is defined in the IEEE
802.3z C36 I guess that's why the layout matches to what is described
in IEEE 802.3z C37.

-Serge(y)

> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!