tree 76cf7270ca64b1d50e43bed33a5413a383b06cd2
parent 119b6658ce050a40a89c12fa88cd9dc4932b1a9f
author Richard Watts <rrw@kynesim.co.uk> 1480713278 +0200
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1483697769 +0100

clk: ti: omap36xx: Work around sprz319 advisory 2.1

commit 035cd485a47dda64f25ccf8a90b11a07d0b7aa7a upstream.

The OMAP36xx DPLL5, driving EHCI USB, can be subject to a long-term
frequency drift. The frequency drift magnitude depends on the VCO update
rate, which is inversely proportional to the PLL divider. The kernel
DPLL configuration code results in a high value for the divider, leading
to a long term drift high enough to cause USB transmission errors. In
the worst case the USB PHY's ULPI interface can stop responding,
breaking USB operation completely. This manifests itself on the
Beagleboard xM by the LAN9514 reporting 'Cannot enable port 2. Maybe the
cable is bad?' in the kernel log.

Errata sprz319 advisory 2.1 documents PLL values that minimize the
drift. Use them automatically when DPLL5 is used for USB operation,
which we detect based on the requested clock rate. The clock framework
will still compute the PLL parameters and resulting rate as usual, but
the PLL M and N values will then be overridden. This can result in the
effective clock rate being slightly different than the rate cached by
the clock framework, but won't cause any adverse effect to USB
operation.

Signed-off-by: Richard Watts <rrw@kynesim.co.uk>
[Upported from v3.2 to v4.9]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Adam Ford <aford173@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>