Messages in this thread | | | Date | Mon, 3 Apr 2023 10:57:04 +0100 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: Enable USXGMII mode for J784S4 CPSW9G |
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On Mon, Apr 03, 2023 at 03:19:24PM +0530, Siddharth Vadapalli wrote: > > > On 03/04/23 14:29, Russell King (Oracle) wrote: > > On Mon, Apr 03, 2023 at 02:11:08PM +0530, Siddharth Vadapalli wrote: > >> > >> > >> On 03/04/23 14:02, Russell King (Oracle) wrote: > >>> On Mon, Apr 03, 2023 at 11:57:21AM +0530, Siddharth Vadapalli wrote: > >>>> Hello Russell, > >>>> > >>>> On 31/03/23 19:16, Siddharth Vadapalli wrote: > >>>>> > >>>>> > >>>>> On 31-03-2023 16:42, Russell King (Oracle) wrote: > >>>>>> 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? > >>>> > >>>> While the CPSW MAC supports RGMII in-band status operation, the link partner > >>>> might not support it. I have also observed that forced mode is preferred to > >>>> in-band mode as implemented for another driver: > >>>> commit ade64eb5be9768e40c90ecb01295416abb2ddbac > >>>> net: dsa: microchip: Disable RGMII in-band status on KSZ9893 > >>>> > >>>> and in the mail thread at: > >>>> https://lore.kernel.org/netdev/20200905160647.GJ3164319@lunn.ch/ > >>>> based on Andrew's suggestion, using forced mode appears to be better. > >>>> > >>>> Additionally, I have verified that switching to in-band status causes a > >>>> regression. Thus, I will prefer keeping it in forced mode for 100 and 1000 Mbps > >>>> RGMII mode which is the existing implementation in the driver. Please let me know. > >>> > >>> Okay, so what this seems to mean is if you have a PHY that does not > >>> support in-band status in RGMII mode, then 10Mbps isn't possible - > >>> because the MAC requires in-band status mode to select 10Mbps. > >>> To put it another way, in such a combination, 10Mbps link modes > >>> should not be advertised, nor should they be reported to userspace > >>> as being supported. > >>> > >>> Is that correct? > >> > >> Yes, if the PHY does not support in-band status, 10 Mbps RGMII will not work, > >> despite the MAC supporting 10 Mbps in-band RGMII. However, I notice the following: > >> If the RGMII interface speed is set to 10 Mbps via ethtool, but the: > >> managed = "in-band-status"; > >> property is not mentioned in the device-tree, the interface is able to work with > >> 10 Mbps mode with the PHY. This is with the CPSW MAC configured for in-band mode > >> of operation at 10 Mbps RGMII mode. Please let me know what this indicates, > >> since it appears to me that 10 Mbps is functional in this special case (It might > >> be an erroneous configuration). > > > > I think you need to check carefully what is going on. > > > > Firstly, if you as the MAC is choosing to enable in-band status mode, > > but phylink isn't using in-band status mode, that is entirely a matter > > for your MAC driver. > > > > Secondly, you need to research what the PHY does during the inter-frame > > time (when in-band status would be transferred). This is when RX_CTL > > is 0,0, RX_DV is 0, RX_ER is 0. > > > > For in-band 10Mbps mode to work, RXD nibbles would need to be x001 > > (middle two bits indicate RX clock = 2.5MHz clock for 10Mbps, lsb > > indicates link up). MSB determines duplex. Remember that 10Mbps can > > appear to work with mismatched duplex settings but can cause chaos on > > networks when it disagrees with what the rest of the network is doing. > > > > So, I think before one says "setting in-band mode for 10Mbps with a > > PHY that doesn't support in-band" really needs caution and research > > to check what _actually_ ends up happening, and whether it is really > > correct to do this. > > Thank you for the detailed explanation. I will analyze it and fix this. In the > meanwhile, is it acceptable for me to post the v2 of this series, with the other > suggestions implemented, while maintaining the status quo for the 10 Mbps RGMII > configuration in the driver? Please let me know.
Yes, but I would like a comment against the bit of code that enables in-band mode indicating that it's questionable whether it is correct.
Thanks.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
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