linux-kernel - Re: [PATCH] net: macb: ignore tx

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Message-ID: <bd029c647db42e05bf1a54d43d601861@walle.cc>
Date:   Thu, 21 Jan 2021 10:41:26 +0100
From:   Michael Walle <michael@...le.cc>
To:     Claudiu.Beznea@...rochip.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicolas.Ferre@...rochip.com, davem@...emloft.net
Subject: Re: [PATCH] net: macb: ignore tx_clk if MII is used

Hi Claudiu,

Am 2021-01-21 10:19, schrieb Claudiu.Beznea@...rochip.com:
> On 20.01.2021 21:43, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
>> the content is safe
>> 
>> If the MII interface is used, the PHY is the clock master, thus don't
>> set the clock rate. On Zynq-7000, this will prevent the following
>> warning:
>>   macb e000b000.ethernet eth0: unable to generate target frequency: 
>> 25000000 Hz
>> 
> 
> Since in this case the PHY provides the TX clock and it provides the 
> proper
> rate based on link speed, the MACB driver should not handle the 
> bp->tx_clk
> at all (MACB driver uses this clock only for setting the proper rate on 
> it
> based on link speed). So, I believe the proper fix would be to not pass 
> the
> tx_clk at all in device tree. This clock is optional for MACB driver.

Thanks for looking into this.

I had the same thought. But shouldn't the driver handle this case 
gracefully?
I mean it does know that the clock isn't needed at all. Ususually that 
clock
is defined in a device tree include. So you'd have to redefine that node 
in
an actual board file which means duplicating the other clocks.

-michael