Subject: Re: [PATCH net-next v2 1/3] net: ethernet: fec: Replace interrupt driven MDIO with polled IO

From: Florian Fainelli <[email-masked]>
Date: Sat, 18 Apr 2020 14:06:44 -0700

On 4/17/2020 5:03 PM, Andrew Lunn wrote:
> Measurements of the MDIO bus have shown that driving the MDIO bus
> using interrupts is slow. Back to back MDIO transactions take about
> 90uS, with 25uS spent performing the transaction, and the remainder of
> the time the bus is idle.
> 
> Replacing the completion interrupt with polled IO results in back to
> back transactions of 40uS. The polling loop waiting for the hardware
> to complete the transaction takes around 27uS. Which suggests
> interrupt handling has an overhead of 50uS, and polled IO nearly
> halves this overhead, and doubles the MDIO performance.
> 
> Suggested-by: Chris Heally <[email-masked]>
> Signed-off-by: Andrew Lunn <[email-masked]>

You should support both modes and let an user decide whether they want 
to use interrupts or polling mode by specifying or omitting the 
'interrupts' property in their Device Tree.
-- 
Florian