netdev - Re: [PATCH net-next 2/3] net: stmmac: xgmac: Correct supported speed modes

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Message-ID: <74770df8-007a-45de-b77e-6aa491bbb2ae@altera.com>
Date: Thu, 17 Jul 2025 18:29:33 +0530
From: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Romain Gantois <romain.gantois@...tlin.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Matthew Gerlach <matthew.gerlach@...era.com>
Subject: Re: [PATCH net-next 2/3] net: stmmac: xgmac: Correct supported speed
 modes

Hi Serge,

Thanks for the review comments and the detailed explanation.

On 7/17/2025 5:17 PM, Serge Semin wrote:
> On Tue, Jul 15, 2025 at 07:03:58PM +0530, G Thomas, Rohan wrote:
>> Hi Andrew,
>>
>> Thanks for reviewing the patch.
>>
>> On 7/14/2025 7:12 PM, Andrew Lunn wrote:
>>> On Mon, Jul 14, 2025 at 03:59:18PM +0800, Rohan G Thomas via B4 Relay wrote:
>>>> From: Rohan G Thomas <rohan.g.thomas@...era.com>
>>>>
>>>> Correct supported speed modes as per the XGMAC databook.
>>>> Commit 9cb54af214a7 ("net: stmmac: Fix IP-cores specific
>>>> MAC capabilities") removes support for 10M, 100M and
>>>> 1000HD. 1000HD is not supported by XGMAC IP, but it does
>>>> support 10M and 100M FD mode, and it also supports 10M and
>>>> 100M HD mode if the HDSEL bit is set in the MAC_HW_FEATURE0
>>>> reg. This commit adds support for 10M and 100M speed modes
>>>> for XGMAC IP.
>>>
>>>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
>>>> @@ -405,6 +405,7 @@ static int dwxgmac2_get_hw_feature(void __iomem *ioaddr,
>>>>    	dma_cap->sma_mdio = (hw_cap & XGMAC_HWFEAT_SMASEL) >> 5;
>>>>    	dma_cap->vlhash = (hw_cap & XGMAC_HWFEAT_VLHASH) >> 4;
>>>>    	dma_cap->half_duplex = (hw_cap & XGMAC_HWFEAT_HDSEL) >> 3;
>>>> +	dma_cap->mbps_10_100 = (hw_cap & XGMAC_HWFEAT_GMIISEL) >> 1;
>>>
>>> The commit message does not mention this change.
>>
>> Agreed. Will do in the next version.
>>
>>>
>>> What does XGMAC_HWFEAT_GMIISEL mean? That a SERDES style interface is
>>> not being used? Could that be why Serge removed these speeds? He was
>>> looking at systems with a SERDES, and they don't support slower
>>> speeds?
>>>
>>> 	Andrew
>> As per the XGMAC databook ver 3.10a, GMIISEL bit of MAC_HW_Feature_0
>> register indicates whether the XGMAC IP on the SOC is synthesized with
>> DWCXG_GMII_SUPPORT. Specifically, it states:
>> "1000/100/10 Mbps Support. This bit is set to 1 when the GMII Interface
>> option is selected."
>>
>> So yes, it’s likely that Serge was working with a SERDES interface which
>> doesn't support 10/100Mbps speeds. Do you think it would be appropriate
>> to add a check for this bit before enabling 10/100Mbps speeds?
> 
> DW XGMAC IP-core of v2.x and older don't support 10/100Mbps modes
> neither in the XGMII nor in the GMII interfaces. That's why I dropped
> the 10/100Mbps link capabilities retaining 1G, 2.5G and 10G speeds
> only (the only speeds supported for DW XGMAC 1.20a/2.11a Tx in the
> MAC_Tx_Configuration.SS register field). Although I should have
> dropped the MAC_5000FD too since it has been supported since v3.0
> IP-core version. My bad.(
> 
> Starting from DW XGMAC v3.00a IP-core the list of the supported speeds
> has been extended to: 10/100Mbps (MII), 1G/2.5G (GMII), 2.5G/5G/10G
> (XGMII). Thus the more appropriate fix here should take into account
> the IP-core version. Like this:
> 	if (dma_cap->mbps_1000 && MAC_Version.SNPSVER >= 0x30)
> 		dma_cap->mbps_10_100 = 1;
>  > Then you can use the mbps_1000 and mbps_10_100 flags to set the proper
> MAC-capabilities to hw->link.caps in the dwxgmac2_setup() method. I
> would have added the XGMII 2.5G/5G MAC-capabilities setting up to the
> dwxgmac2_setup() method too for the v3.x IP-cores and newer.
> 

Agreed. Will do in the next version.

Will ensure that mbps_10_100 is set only if SNPSVER >= 0x30 and will
also conditionally enable 2.5G/5G MAC capabilities for IP versions
v3.00a and above.

In the stmmac_dvr_probe() the setup() callback is invoked before
hw_cap_support is populated. Given that, do you think it is sufficient
to add these checks into the dwxgmac2_update_caps() instead?

> -Serge(y)
> 
>>
>> Best Regards,
>> Rohan
>>

Best Regards,
Rohan