netdev - Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: Enable USXGMII mode for J784S4 CPSW9G

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Message-ID: <ZCbAE7IIc8HcOdxl@shell.armlinux.org.uk>
Date:   Fri, 31 Mar 2023 12:12:19 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Siddharth Vadapalli <s-vadapalli@...com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, rogerq@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        srk@...com
Subject: Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: Enable
 USXGMII mode for J784S4 CPSW9G

On Fri, Mar 31, 2023 at 04:23:16PM +0530, Siddharth Vadapalli wrote:
> 
> 
> On 31/03/23 15:16, Russell King (Oracle) wrote:
> > On Fri, Mar 31, 2023 at 02:55:56PM +0530, Siddharth Vadapalli wrote:
> >> Russell,
> >>
> >> On 31/03/23 13:54, Russell King (Oracle) wrote:
> >>> On Fri, Mar 31, 2023 at 01:35:10PM +0530, Siddharth Vadapalli wrote:
> >>>> Hello Russell,
> >>>>
> >>>> Thank you for reviewing the patch.
> >>>>
> >>>> On 31/03/23 13:27, Russell King (Oracle) wrote:
> >>>>> On Fri, Mar 31, 2023 at 12:21:10PM +0530, Siddharth Vadapalli wrote:
> >>>>>> TI's J784S4 SoC supports USXGMII mode. Add USXGMII mode to the
> >>>>>> extra_modes member of the J784S4 SoC data. Additionally, configure the
> >>>>>> MAC Control register for supporting USXGMII mode. Also, for USXGMII
> >>>>>> mode, include MAC_5000FD in the "mac_capabilities" member of struct
> >>>>>> "phylink_config".
> >>>>>
> >>>>> I don't think TI "get" phylink at all...
> >>>>>
> >>>>>> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> >>>>>> index 4b4d06199b45..ab33e6fe5b1a 100644
> >>>>>> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> >>>>>> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> >>>>>> @@ -1555,6 +1555,8 @@ static void am65_cpsw_nuss_mac_link_up(struct phylink_config *config, struct phy
> >>>>>>  		mac_control |= CPSW_SL_CTL_GIG;
> >>>>>>  	if (interface == PHY_INTERFACE_MODE_SGMII)
> >>>>>>  		mac_control |= CPSW_SL_CTL_EXT_EN;
> >>>>>> +	if (interface == PHY_INTERFACE_MODE_USXGMII)
> >>>>>> +		mac_control |= CPSW_SL_CTL_XGIG | CPSW_SL_CTL_XGMII_EN;
> >>>>>
> >>>>> The configuration of the interface mode should *not* happen in
> >>>>> mac_link_up(), but should happen in e.g. mac_config().
> >>>>
> >>>> I will move all the interface mode associated configurations to mac_config() in
> >>>> the v2 series.
> >>>
> >>> Looking at the whole of mac_link_up(), could you please describe what
> >>> effect these bits are having:
> >>>
> >>> 	CPSW_SL_CTL_GIG
> >>> 	CPSW_SL_CTL_EXT_EN
> >>> 	CPSW_SL_CTL_IFCTL_A
> >>
> >> CPSW_SL_CTL_GIG corresponds to enabling Gigabit mode (full duplex only).
> >> CPSW_SL_CTL_EXT_EN when set enables in-band mode of operation and when cleared
> >> enables forced mode of operation.
> >> CPSW_SL_CTL_IFCTL_A is used to set the RMII link speed (0=10 mbps, 1=100 mbps).
> > 
> > Okay, so I would do in mac_link_up():
> > 
> > 	/* RMII needs to be manually configured for 10/100Mbps */
> > 	if (interface == PHY_INTERFACE_MODE_RMII && speed == SPEED_100)
> > 		mac_control |= CPSW_SL_CTL_IFCTL_A;
> > 
> > 	if (speed == SPEED_1000)
> > 		mac_control |= CPSW_SL_CTL_GIG;
> > 	if (duplex)
> > 		mac_control |= CPSW_SL_CTL_FULLDUPLEX;
> > 
> > I would also make mac_link_up() do a read-modify-write operation to
> > only affect the bits that it is changing.
> 
> This is the current implementation except for the SGMII mode associated
> operation that I had recently added. I will fix that. Also, the
> cpsw_sl_ctl_set() function which writes the mac_control value performs a read
> modify write operation.
> 
> > 
> > Now, for SGMII, I would move setting CPSW_SL_CTL_EXT_EN to mac_config()
> > to enable in-band mode - don't we want in-band mode enabled all the
> > time while in SGMII mode so the PHY gets the response from the MAC?
> 
> Thank you for pointing it out. I will move that to mac_config().
> 
> > 
> > Lastly, for RGMII at 10Mbps, you seem to suggest that you need RGMII
> > in-band mode enabled for that - but if you need RGMII in-band for
> > 10Mbps, wouldn't it make sense for the other speeds as well? If so,
> > wouldn't that mean that CPSW_SL_CTL_EXT_EN can always be set for
> > RGMII no matter what speed is being used?
> 
> The CPSW MAC does not support forced mode at 10 Mbps RGMII. For this reason, if
> RGMII 10 Mbps is requested, it is set to in-band mode.

What I'm saying is that if we have in-band signalling that is reliable
for a particular interface mode, why not always use it, rather than
singling out one specific speed as an exception? Does it not work in
100Mbps and 1Gbps?

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