ACK: [PATCH] net: qcom/emac: do not use hardware mdio automatic polling

[Seth Forshee]

On Tue, Jun 06, 2017 at 05:00:17PM -0500, Manoj Iyer wrote:
> From: Timur Tabi <timur at codeaurora.org>
> 
> Use software polling (PHY_POLL) to check for link state changes instead
> of relying on the EMAC's hardware polling feature.  Some PHY drivers
> are unable to get a functioning link because the HW polling is not
> robust enough.
> 
> The EMAC is able to poll the PHY on the MDIO bus looking for link state
> changes (via the Link Status bit in the Status Register at address 0x1).
> When the link state changes, the EMAC triggers an interrupt and tells the
> driver what the new state is.  The feature eliminates the need for
> software to poll the MDIO bus.
> 
> Unfortunately, this feature is incompatible with phylib, because it
> ignores everything that the PHY core and PHY drivers are trying to do.
> In particular:
> 
> 1. It assumes a compatible register set, so PHYs with different registers
>    may not work.
> 
> 2. It doesn't allow for hardware errata that have work-arounds implemented
>    in the PHY driver.
> 
> 3. It doesn't support multiple register pages. If the PHY core switches
>    the register set to another page, the EMAC won't know the page has
>    changed and will still attempt to read the same PHY register.
> 
> 4. It only checks the copper side of the link, not the SGMII side.  Some
>    PHY drivers (e.g. at803x) may also check the SGMII side, and
>    report the link as not ready during autonegotiation if the SGMII link
>    is still down.  Phylib then waits for another interrupt to query
>    the PHY again, but the EMAC won't send another interrupt because it
>    thinks the link is up.
> 
> BugLink: https://bugs.launchpad.net/bugs/1696143
> 
> Cc: stable at vger.kernel.org # 4.11.x
> Tested-by: Manoj Iyer <manoj.iyer at canonical.com>
> Signed-off-by: Timur Tabi <timur at codeaurora.org>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (cherry picked from commit 246096690be0742d9bb5f3456d2cb95b68f7b46d)
> Signed-off-by: Manoj Iyer <manoj.iyer at canonical.com>

Clean cherry pick, isolated to a single driver, and also an upstream
stable patch.

Acked-by: Seth Forshee <seth.forshee at canonical.com>

Note that this has already been applied to artful/master-next as part of
4.11.5.