netdev - Re: [PATCH net v4 1/5] net: phy: micrel: add Microchip KSZ 9897 Switch PHY support

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Date: Mon, 3 Jun 2024 09:53:40 +0200
From: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@...oirfairelinux.com>
To: Tristram.Ha@...rochip.com
Cc: andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk,
 Woojung.Huh@...rochip.com, UNGLinuxDriver@...rochip.com,
 netdev@...r.kernel.org
Subject: Re: [PATCH net v4 1/5] net: phy: micrel: add Microchip KSZ 9897
 Switch PHY support



On 31/05/2024 21:39, Tristram.Ha@...rochip.com wrote:
> 
> 
>> -----Original Message-----
>> From: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@...oirfairelinux.com>
>> Sent: Friday, May 31, 2024 7:24 AM
>> diff --git a/include/linux/micrel_phy.h b/include/linux/micrel_phy.h
>> index 591bf5b5e8dc..81cc16dc2ddf 100644
>> --- a/include/linux/micrel_phy.h
>> +++ b/include/linux/micrel_phy.h
>> @@ -39,6 +39,10 @@
>>   #define PHY_ID_KSZ87XX         0x00221550
>>
>>   #define        PHY_ID_KSZ9477          0x00221631
>> +/* Pseudo ID to specify in compatible field of device tree.
>> + * Otherwise the device reports the same ID as KSZ8081 on CPU ports.
>> + */
>> +#define        PHY_ID_KSZ9897          0x002217ff
>>
> 
> I am curious about this KSZ9897 device.  Can you point out its product
> page on Microchip website?
> 
> KSZ9897 is typically referred to the KSZ9897 switch family, which
> contains KSZ9897, KSZ9896, KSZ9567, KSZ8567, KSZ9477 and some others.
> 
> I am not aware that KSZ9897 has MDIO access.  The switch is only accessed
> through I2C and SPI and proprietary IBA.
> 
> It seems the only function is just to report link so a fixed PHY should
> be adequate in this situation.
> 
> MDIO only mode is present in KSZ8863/KSZ8873 switches.  I do not know
> useful to use such mode in KSZ9897.
> 

I'm using the KSZ9897R from this page:
  - https://www.microchip.com/en-us/product/ksz9897

My CPU (i.MX6ULL) is connected to the CPU port 6 in RMII, listed in "Two 
Configurable External MAC Ports" with RGMII. This is for network 
connectivity with the switch, while I'm using SPI for DSA control. 
FIGURE 2-1 illustrates that architecture. However, this MDIO interface 
is indeed missing some documentation. For instance, it's phy_id is never 
listed (Section 5.2.2.3 only for ports 1-5).

I use a fixed-link property in the device tree, but the link would never 
come up if I use the KSZ8081 PHY driver which was selected without these 
patches because it emits the same phy_id as port 6. The genphy and 
KSZ9477 PHY dirvers were no better. I found out that the KSZ8873MLL 
driver was compatible though, which seems to make sense given your 
explanation.

-- 
Savoir-faire Linux
Enguerrand de Ribaucourt