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: <i6i5q64zfji3ohwsi3ikybpjulcbfce7zjgh3y44zj5gv4rqmp@jvzptfeotz2m>
Date:   Tue, 31 Oct 2023 03:56:29 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
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 01:40:34PM +0100, Russell King (Oracle) wrote:
> 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.

Thanks for the detailed response. I'll send fixup patches for the
denoted problems as soon as I get some free time for it. Hopefully
within a month if nobody does it sooner.

-Serge(y)

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