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

Jie Luo
2024-02-05T03:24:41Z

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.