Re: [PATCH net-next v2] net: phy: dp83867: Add speed optimization feature

From: Dan Murphy
Date: Tue Feb 18 2020 - 11:41:42 EST


On 2/18/20 10:25 AM, Russell King - ARM Linux admin wrote:
On Fri, Feb 14, 2020 at 12:31:52PM -0600, Dan Murphy wrote:

On 2/14/20 12:32 PM, Grygorii Strashko wrote:
I think it's good idea to have this message as just wrong cable might be

But this notifier make no sense in it current form - it will produce
noise in case of forced 100m/10M.

FYI. PHY sequence to update link:
ÂÂÂ |- .phy_link_change()->phy_link_change()
ÂÂÂÂ|-adjust_link() ----> netdev callback

So, log output has to be done or in .read_status() or
some info has to be saved in .read_status() and then re-used in

OK I will try to find a way to give some sort of message.
How do you know the speed that the PHY downshifted to?

The DP83867 has a register PHYSTS where BIT 15:14 indicate the speed that the PHY negotiated.

In the same register BIT 13 indicates the duplex mode.

If the speed and duplex are available in some PHY specific status
register, then one way you can detect downshift is to decode the
negotiated speed/duplex from the advertisements (specifically the LPA
read from the registers and the advertisement that we should be
advertising - some PHYs modify their registers when downshifting) and
check whether it matches the negotiated parameters in the PHY
specific status register.

Alternatively, if the PHY modifies the advertisement register on
downshift, comparing the advertisement register with what it should
be will tell you if downshift has occurred.

The ISR register BIT 5 indicates if a downshift occurred or not. So we can indicate that the PHY downshifted but there is no cause in the registers bit field. My concern for this bit though is the register is clear on read so all other interrupts are lost if we only read to check downshift. And the link_change_notifier is called before the interrupt ACK call back. We could call the interrupt function and get the downshift status but again it will clear the interrupt register and any other statuses may be lost.