Merge branch 'Fix-regression-with-AR8035-speed-downgrade'
Russell King says: ==================== Fix regression with AR8035 speed downgrade The following series attempts to address an issue spotted by tinywrkb with the AR8035 on the Cubox-i2 in a situation where the PHY downgrades the negotiated link. This is version 2, not much has changed other than rebasing on the current net tree. Changes have happend to patch 2 due to conflicts, so I dropped Andrew's reviewed-by. Minor context changes to patch 4 which I don't consider important enough to warrant dropping the reviewed-by. Before commit 5502b218 ("net: phy: use phy_resolve_aneg_linkmode in genphy_read_status"), we would read not only the link partner's advertisement, but also our own advertisement from the PHY registers, and use both to derive the PHYs current link mode. This works when the AR8035 downgrades the speed, because it appears that the AR8035 clears link mode bits in the advertisement registers as part of the downgrade. Commentary: what is not yet known is whether the AR8035 restores the advertisement register when the link goes down to the previous state. However, since the above referenced commit, we no longer use the PHYs advertisement registers, instead converting the link partner's advertisement to the ethtool link mode array, and combine that with phylib's cached version of our advertisement - which is not updated on speed downgrade. This results in phylib disagreeing with the actual operating mode of the PHY. Commentary: I wonder how many more PHY drivers are broken by this commit, but have yet to be discovered. The obvious way to address this would be to disable the downgrade feature, and indeed this does fix the problem in tinywrkb's case - his link partner instead downgrades the speed by reducing its advertisement, resulting in phylib correctly evaluating a slower speed. However, it has a serious drawback - the gigabit control register (MII register 9) appears to become read only. It seems the only way to update the register is to re-enable the downgrade feature, reset the PHY, changing register 9, disable the downgrade feature, and reset the PHY again. This series attempts to address the problem using a different approach, similar to the approach taken with Marvell PHYs. The AR8031, AR8033 and AR8035 have a PHY-Specific Status register which reports the actual operating mode of the PHY - both speed and duplex. This register correctly reports the operating mode irrespective of whether autoneg is enabled or not. We use this register to fill in phylib's speed and duplex parameters. In detail: Patch 1 fixes a bug where writing to register 9 does not update phylib's advertisement mask in the same way that writing register 4 does; this looks like an omission from when gigabit PHY support came into being. Patch 2 seperates the generic phylib code which reads the link partners advertisement from the PHY, so that we can re-use this in the Atheros PHY driver. Patch 3 seperates the generic phylib pause mode; phylib provides no help for MAC drivers to ascertain the negotiated pause mode, it merely copies the link partner's pause mode bits into its own variables. Commentary: Both the aforementioned Atheros PHYs and Marvell PHYs provide the resolved pause modes in terms of whether we should transmit pause frames, or whether we should allow reception of pause frames. Surely the resolution of this should be in phylib? Patch 4 provides the Atheros PHY driver with a private "read_status" implementation that fills in phylib's speed and duplex settings depending on the PHY-Specific status register. This ensures that phylib and the MAC driver match the operating mode that the PHY has decided to use. Since the register also gives us MDIX status, we can trivially fill that status in as well. Note that, although the bits mentioned in this patch for this register match those in th Marvell PHY driver, and it is located at the same address, the meaning of other register bits varies between the PHYs. Therefore, I do not feel that it would be appropriate to make this some kind of generic function. ==================== Signed-off-by: David S. Miller <firstname.lastname@example.org>
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