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Petr Oros e96bd2d3b1 phy: avoid unnecessary link-up delay in polling mode 
commit 93c0970493 ("net: phy: consider latched link-down status in
polling mode") removed double-read of latched link-state register for
polling mode from genphy_update_link(). This added extra ~1s delay into
sequence link down->up.
Following scenario:
 - After boot link goes up
 - phy_start() is called triggering an aneg restart, hence link goes
   down and link-down info is latched.
 - After aneg has finished link goes up. In phy_state_machine is checked
   link state but it is latched "link is down". The state machine is
   scheduled after one second and there is detected "link is up". This
   extra delay can be avoided when we keep link-state register double read
   in case when link was down previously.

With this solution we don't miss a link-down event in polling mode and
link-up is faster.

Details about this quirky behavior on Realtek phy:
Without patch:
T0:    aneg is started, link goes down, link-down status is latched
T0+3s: state machine runs, up-to-date link-down is read
T0+4s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1),
       here i read link-down (BMSR_LSTATUS==0),
T0+5s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1),
       up-to-date link-up is read (BMSR_LSTATUS==1),
       phydev->link goes up, state change PHY_NOLINK to PHY_RUNNING

With patch:
T0:    aneg is started, link goes down, link-down status is latched
T0+3s: state machine runs, up-to-date link-down is read
T0+4s: state machine runs, aneg is finished (BMSR_ANEGCOMPLETE==1),
       first BMSR read: BMSR_ANEGCOMPLETE==1 and BMSR_LSTATUS==0,
       second BMSR read: BMSR_ANEGCOMPLETE==1 and BMSR_LSTATUS==1,
       phydev->link goes up, state change PHY_NOLINK to PHY_RUNNING

Signed-off-by: Petr Oros <poros@redhat.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
History 2020-02-19 16:17:28 -08:00
arch arm64: time: Replace <linux/clk-provider.h> by <linux/of_clk.h> 2020-02-12 17:26:38 +00:00
block block-5.6-2020-02-05 2020-02-06 06:15:23 +00:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-02-13 14:17:39 -08:00
Documentation Kbuild updates for v5.6 (2nd) 2020-02-09 16:05:50 -08:00
drivers phy: avoid unnecessary link-up delay in polling mode 2020-02-19 16:17:28 -08:00
fs dax fixes 5.6-rc1 2020-02-11 16:52:08 -08:00
include net: core: add helper tcp_v6_gso_csum_prep 2020-02-19 11:20:59 -08:00
init Various fixes: 2020-02-11 16:39:18 -08:00
ipc proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
kernel Power management fixes for 5.6-rc2 2020-02-14 12:34:30 -08:00
lib lib: objagg: Replace zero-length arrays with flexible-array member 2020-02-16 18:33:00 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Merge branch 'merge.nfs-fs_parse.1' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-02-08 13:26:41 -08:00
net net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns 2020-02-19 11:04:31 -08:00
samples Kbuild updates for v5.6 (2nd) 2020-02-09 16:05:50 -08:00
scripts kbuild: fix mismatch between .version and include/generated/compile.h 2020-02-11 05:18:40 +09:00
security selinux/stable-5.6 PR 20200210 2020-02-10 16:51:35 -08:00
sound ALSA: pcm: Fix double hw_free calls 2020-02-13 16:30:22 +01:00
tools selftests: mlxsw: vxlan: Add test for error path 2020-02-17 14:42:53 -08:00
usr Kbuild updates for v5.6 (2nd) 2020-02-09 16:05:50 -08:00
virt KVM: fix overflow of zero page refcount with ksm running 2020-02-05 15:27:46 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap A handful of small documentation fixes that wandered in. 2020-02-07 13:03:10 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS open: introduce openat2(2) syscall 2020-01-18 09:19:18 -05:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Sort entries in database for GPIO 2020-02-10 10:55:18 +01:00
Makefile Linux 5.6-rc1 2020-02-09 16:08:48 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.