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

[Dan Murphy]

Heiner

On 2/5/20 3:16 PM, Heiner Kallweit wrote:
> On 04.02.2020 19:13, Dan Murphy wrote:
> > Set the speed optimization bit on the DP83867 PHY.
> > This feature can also be strapped on the 64 pin PHY devices
> > but the 48 pin devices do not have the strap pin available to enable
> > this feature in the hardware.  PHY team suggests to have this bit set.
> >
> > With this bit set the PHY will auto negotiate and report the link
> > parameters in the PHYSTS register.  This register provides a single
> > location within the register set for quick access to commonly accessed
> > information.
> >
> > In this case when auto negotiation is on the PHY core reads the bits
> > that have been configured or if auto negotiation is off the PHY core
> > reads the BMCR register and sets the phydev parameters accordingly.
> >
> > This Giga bit PHY can throttle the speed to 100Mbps or 10Mbps to accomodate a
> > 4-wire cable.  If this should occur the PHYSTS register contains the
> > current negotiated speed and duplex mode.
> >
> > In overriding the genphy_read_status the dp83867_read_status will do a
> > genphy_read_status to setup the LP and pause bits.  And then the PHYSTS
> > register is read and the phydev speed and duplex mode settings are
> > updated.
> >
> > Signed-off-by: Dan Murphy <dmurphy@xxxxxx>
> > ---
> > v2 - Updated read status to call genphy_read_status first, added link_change
> > callback to notify of speed change and use phy_set_bits - https://lore.kernel.org/patchwork/patch/1188348/
> As stated in the first review, it would be appreciated if you implement
> also the downshift tunable. This could be a separate patch in this series.
> Most of the implementation would be boilerplate code.


I looked at this today and there are no registers that allow tuning the 
downshift attempts. There is only a RO register that tells you how many 
attempts it took to achieve a link. So at the very least we could put 
in the get_tunable but there will be no set.

So we should probably skip this for this PHY.

Dan