Re: [PATCH v3] clk: ti: omap36xx: Work around sprz319 advisory 2.1

[Stephen Boyd <sboyd@codeaurora.org>]

On 01/03, Adam Ford wrote:
> On Thu, Dec 8, 2016 at 3:24 PM, Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> wrote:
> > Hi Stephen,
> >
> > On Thursday 08 Dec 2016 13:16:01 Stephen Boyd wrote:
> >> On 12/02, Laurent Pinchart wrote:
> >> > From: Richard Watts <rrw@kynesim.co.uk>
> >> >
> >> > 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>
> >> > ---
> >>
> >> Applied to clk-next
> >
> 
> Since this fixes an errata issue, is there any way we can get this
> patch applied to the older LTS kernels?  (4.4 seems to apply cleanly,
> but I didn't try any older than that)
> 

Sure. Just follow the stable kernel rules. See
Documentation/process/stable-kernel-rules.rst, specifically
option #2.

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