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Date:   Fri, 31 Mar 2023 19:16:55 +0530
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Subject: Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: Enable USXGMII
 mode for J784S4 CPSW9G
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
References: <20230331065110.604516-1-s-vadapalli@ti.com>
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From:   Siddharth Vadapalli <s-vadapalli@ti.com>
In-Reply-To: <ZCbAE7IIc8HcOdxl@shell.armlinux.org.uk>
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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?

In-band RGMII is supported for speeds of 10, 100 and 1000 Mbps.
Unfortunately, I am not aware of the reason why RGMII at speeds 100 and
1000 Mbps was implemented in the driver in forced mode. As suggested by
you, I will work on implementing it in in-band mode for all speeds and
verify that it works, following which I will post the v2 of this series,
with the following changes based on your feedback:
1. All interface mode specific configuration will be moved to mac_config().
2. Since CPSW MAC supports USXGMII mode, MAC_5000FD will be added to the
list of mac_capabilites unconditionally, unlike the current implementation.
3. In-band mode of operation will be enabled for all interface modes by
default.

Regards,
Siddharth.