Re: [PATCH net-next] net: phy: sfp: handle cases where neither BR,min nor BR,max is given

[Antoine Tenart <antoine.tenart@bootlin.com>]

Hi Russell,

On Tue, May 08, 2018 at 01:30:26PM +0100, Russell King - ARM Linux wrote:
> 
> The electronic engineer in me says that using zero isn't really valid
> because there are coupling capacitors in the SFP module that block DC.
> These blocking capacitors are required by the SFP+ specs to have a high
> pass pole of between 20kHz and 100kHz - in other words, frequencies
> below this are attenuated by the coupling capacitors.  The relationship
> between this and the bit rate will be a function of the encoding, so we
> can't come to a definitive figure without some math (and I want to be
> lazy about that!)
> 
> Practically, we're talking about SerDes Ethernet, where the bit rate is
> no lower than 100Mbps [*], which will always have a frequency well above
> this cut-off.  So, I don't have any problem with your approach to
> setting the minimum to zero.  Therefore,
> 
> Acked-by: Russell King <rmk+kernel@armlinux.org.uk>

Thanks for looking into it!
Antoine


-- 
Antoine Ténart, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com