linux-kernel - Re: [PATCH net-next V3] net: pcs: xpcs: Add 2500BASE-X case in get state for XPCS drivers

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Message-ID: <ZTuvwnGZKEueGDwa@shell.armlinux.org.uk>
Date:   Fri, 27 Oct 2023 13:40:34 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Raju Lakkaraju <Raju.Lakkaraju@...rochip.com>,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        linux-kernel@...r.kernel.org, andrew@...n.ch,
        Jose.Abreu@...opsys.com, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next V3] net: pcs: xpcs: Add 2500BASE-X case in get
 state for XPCS drivers

On Fri, Oct 27, 2023 at 03:06:19PM +0300, Serge Semin wrote:
> Hi Russell
> 
> On Fri, Oct 27, 2023 at 12:54:36PM +0100, Russell King (Oracle) wrote:
> > On Fri, Oct 27, 2023 at 02:04:15PM +0300, Serge Semin wrote:
> > > Cc += Russell
> > > 
> > > * It's a good practice to add all the reviewers to Cc in the new patch
> > > * revisions.
> > > 
> > > On Fri, Oct 27, 2023 at 10:13:06AM +0530, Raju Lakkaraju wrote:
> > > > Add DW_2500BASEX case in xpcs_get_state( ) to update speed, duplex and pause
> > > > 
> > > > Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@...rochip.com>
> > > 
> > > With a nitpick below clarified, feel free to add:
> > > Reviewed-by: Serge Semin <fancer.lancer@...il.com>
> > > 
> > > > ---
> > > >  drivers/net/pcs/pcs-xpcs.c | 29 +++++++++++++++++++++++++++++
> > > >  drivers/net/pcs/pcs-xpcs.h |  2 ++
> > > >  2 files changed, 31 insertions(+)
> > > > 
> > > > diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
> > > > index 4dbc21f604f2..31f0beba638a 100644
> > > > --- a/drivers/net/pcs/pcs-xpcs.c
> > > > +++ b/drivers/net/pcs/pcs-xpcs.c
> > > > @@ -1090,6 +1090,28 @@ static int xpcs_get_state_c37_1000basex(struct dw_xpcs *xpcs,
> > > >  	return 0;
> > > >  }
> > > >  
> > > > +static int xpcs_get_state_2500basex(struct dw_xpcs *xpcs,
> > > > +				    struct phylink_link_state *state)
> > > > +{
> > > > +	int ret;
> > > > +
> > > > +	ret = xpcs_read(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_STS);
> > > > +	if (ret < 0) {
> > > > +		state->link = 0;
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	state->link = !!(ret & DW_VR_MII_MMD_STS_LINK_STS);
> > > > +	if (!state->link)
> > > > +		return 0;
> > > > +
> > > > +	state->speed = SPEED_2500;
> > > 
> > > > +	state->pause |= MLO_PAUSE_TX | MLO_PAUSE_RX;
> > > 
> > > Why is it '|=' instead of just '='? Is it possible to have the 'pause'
> > > field having some additional flags set which would be required to
> > > preserve?
> > 
> > The code is correct. There are other flags on state->pause other than
> > these, and phylink initialises state->pause prior to calling the
> > function. The only flags that should be modified here are these two
> > bits that the code is setting.
> > 
> > Phylink will initialise it to MLO_PAUSE_NONE if expecting autoneg, or
> > the configured values if autoneg on the link is disabled.
> 
> Thanks for clarification. Then no more comments from my side in this
> patch regard.
> 
> Regarding the XPCS driver in general. Based on what you said the rest
> of the XPCS state getters are wrong in fully re-writing the 'pause'
> field. Right?

Yes.

xpcs_resolve_pma:
        state->pause = MLO_PAUSE_TX | MLO_PAUSE_RX;

xpcs_get_state_c37_sgmii:
        state->pause = 0;

are both incorrect. The former should be |=, the latter is totally
unnecessary.

Documentation:
 * pcs_get_state() - Read the current inband link state from the hardware
 * @pcs: a pointer to a &struct phylink_pcs.
 * @state: a pointer to a &struct phylink_link_state.
 *
 * Read the current inband link state from the MAC PCS, reporting the
 * current speed in @state->speed, duplex mode in @state->duplex, pause
                                                                  ^^^^^
 * mode in @state->pause using the %MLO_PAUSE_RX and %MLO_PAUSE_TX bits,
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I guess I need to make that more explicit that pcs_get_state() methods
are only expected to _set_ these two bits as appropriate, leaving all
other bits as-is.

-- 
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