netdev - Re: [net-next PATCH v2 2/3] net: mdio: ipq4019: add support for clock-frequency property

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Message-ID: <05253a6d-7fa5-4c32-af6f-cda0f902cf77@quicinc.com>
Date: Mon, 5 Feb 2024 11:24:16 +0800
From: Jie Luo <quic_luoj@...cinc.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Christian Marangi <ansuelsmth@...il.com>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni
	<pabeni@...hat.com>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Robert Marko <robert.marko@...tura.hr>,
        <linux-arm-msm@...r.kernel.org>, <netdev@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [net-next PATCH v2 2/3] net: mdio: ipq4019: add support for
 clock-frequency property



On 2/4/2024 11:22 PM, Andrew Lunn wrote:
> On Sun, Feb 04, 2024 at 05:59:10PM +0800, Jie Luo wrote:
>>
>>
>> On 1/30/2024 8:35 AM, Christian Marangi wrote:
>>> +
>>> +	/* If div is /256 assume nobody have set this value and
>>> +	 * try to find one MDC rate that is close the 802.3 spec of
>>> +	 * 2.5MHz
>>> +	 */
>>> +	for (div = 256; div >= 8; div /= 2) {
>>> +		/* Stop as soon as we found a divider that
>>> +		 * reached the closest value to 2.5MHz
>>> +		 */
>>> +		if (DIV_ROUND_UP(ahb_rate, div) > 2500000)
>>> +			break;
>>
>> Hi Christian,
>> Sorry for the delayed review.
>>
>> The MDIO hardware block supports higher frequency 6.25M and 12.5M,
>> Would you remove this 2.5MHZ limitation? On the IPQ platform, we
>> normally use 6.25MHZ.
> 
> 802.3 says the clock has a maximum of 2.5MHz. So this code is correct.
> 
> It is however O.K. to go faster, but since that breaks the standard,
> you need each board to indicate it knows all the devices on the bus do
> support higher speeds and its O.K. to break the standard. You indicate
> this by using the DT property in its .dts file. For an MDIO bus which
> is totally internal, you could however put the DT property in the SoC
> .dtsi file.
> 
>        Andrew

Understand it, Thanks Andrew.