Messages in this thread |  | | Subject | Re: [PATCH net-next v2] net: phy: dp83867: Add speed optimization feature | From | Dan Murphy <> | Date | Thu, 6 Feb 2020 16:36:23 -0600 |
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Heiner
On 2/6/20 4:28 PM, Heiner Kallweit wrote: > On 06.02.2020 23:13, Dan Murphy wrote: >> 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@ti.com> >>>> --- >>>> 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. >> > The get operation for the downshift tunable should return after how many failed > attempts the PHY starts a downshift. This doesn't match with your description of > this register, so yes: Implementing the tunable for this PHY doesn't make sense. True. This register is only going to return 1,2,4 and 8. And it is defaulted to 4 attempts. > > However this register may be useful in the link_change_notify() callback to > figure out whether a downshift happened, to trigger the info message you had in > your first version.
Thats a good idea but.. The register is defaulted to always report 4 attempts were made. It never reports 0 attempts so we would never know the truth behind the reporting. Kinda like matching the speeds.
Dan
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