netdev - RE: [PATCH net] net: ethernet: renesas: rswitch Fix PHY station management clock setting

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Date: Wed, 27 Sep 2023 23:58:13 +0000
From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To: Andrew Lunn <andrew@...n.ch>
CC: "s.shtylyov@....ru" <s.shtylyov@....ru>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, Tam
 Nguyen <tam.nguyen.xa@...esas.com>, Kuninori Morimoto
	<kuninori.morimoto.gx@...esas.com>
Subject: RE: [PATCH net] net: ethernet: renesas: rswitch Fix PHY station
 management clock setting

Hello Andrew,

> From: Andrew Lunn, Sent: Wednesday, September 27, 2023 9:11 PM
> 
> > Yes, the original version was tested on Spider board.
> > The original version's MDC frequency was 25MHz.
> > And the PHY (Marvell 88E2110) on Spider board can use such frequency,
> > IIUC because the MDC period is 35 ns (so 28.57143MHz).
> 
> 25MHz is way above anything i've tested.
> 
> > However, I don't know why this setting cannot work on the Starter Kit board
> > because the board also has the same PHY. I guess that this is related to
> > board design, especially voltage of I/O (Spider = 1.8V, Starter Kit = 3.3V).
> 
> I've had boards which will not work at 2.5Mhz until the pull up
> resistor was changed to make the waveform compliant. So it probably is
> related to the board.

I got it.

> > Anyway, changing the MDC frequency from 25MHz to 2.5MHz works correctly on
> > both Spider and Starter Kit. So, I would like to apply the v3 patch [1] for safe.
> 
> O.K. That makes sense. If you want to support the higher speed, you
> could implement the device tree property:
> 
> 
>   clock-frequency:
>     description:
>       Desired MDIO bus clock frequency in Hz. Values greater than IEEE 802.3
>       defined 2.5MHz should only be used when all devices on the bus support
>       the given clock speed.

Thank you for the information. If I need to support the higher speed,
I'll implement such a code with this device tree property.

Best regards,
Yoshihiro Shimoda

> 	Andrew