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| author | Serge Semin <fancer.lancer@gmail.com> | 2019-04-24 17:49:14 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-04-25 10:59:03 +0200 |
| commit | 6e3c8beb4f92a18a65e521cc5fe75874b6e2c860 (patch) | |
| tree | 64ca312a4339f93ba3606172b92ffb514205d01b /tools/perf/scripts/python/export-to-sqlite.py | |
| parent | 77a4946516fe488b6a33390de6d749f934a243ba (diff) | |
usb: usb251xb: Lock i2c-bus segment the hub resides
SMBus slave configuration is activated by CFG_SEL[1:0]=0x1 pins
state. This is the mode the hub is supposed to be to let this driver
work correctly. But a race condition might happen right after reset
is cleared due to CFG_SEL[0] pin being multiplexed with SMBus SCL
function. In case if the reset pin is handled by a i2c GPIO expander,
which is also placed at the same i2c-bus segment as the usb251x
SMB-interface connected to, then the hub reset clearance might
cause the CFG_SEL[0] being latched in unpredictable state. So
sometimes the hub configuration mode might be 0x1 (as expected),
but sometimes being 0x0, which doesn't imply to have the hub SMBus-slave
interface activated and consequently causes this driver failure.
In order to fix the problem we must make sure the GPIO-reset chip doesn't
reside the same i2c-bus segment as the SMBus-interface of the hub. If
it doesn't, we can safely block the segment for the time the reset is
cleared to prevent anyone generating a traffic at the i2c-bus SCL lane
connected to the CFG_SEL[0] pin. But if it does, nothing we can do, so
just return an error. If we locked the i2c-bus segment and tried to
communicate with the GPIO-expander, it would cause a deadlock. If we didn't
lock the i2c-bus segment, it would randomly cause the CFG_SEL[0] bit flip.
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'tools/perf/scripts/python/export-to-sqlite.py')
0 files changed, 0 insertions, 0 deletions