Re: [PATCH] net: macb: ignore tx_clk if MII is used

From: Michael Walle
Date: Thu Jan 21 2021 - 04:43:31 EST

Hi Claudiu,

Am 2021-01-21 10:19, schrieb Claudiu.Beznea@xxxxxxxxxxxxx:
On 20.01.2021 21:43, Michael Walle wrote:
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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
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.