On Tuesday 03 Jan 2017 10:49:56 Stephen Boyd wrote: > On 01/03, Adam Ford wrote: > > On Thu, Dec 8, 2016 at 3:24 PM, Laurent Pinchart wrote: > >> On Thursday 08 Dec 2016 13:16:01 Stephen Boyd wrote: > >>> On 12/02, Laurent Pinchart wrote: > >>>> From: Richard Watts <rrw@xxxxxxxxxxxxx> > >>>> > >>>> 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@xxxxxxxxxxxxx> > >>>> [Upported from v3.2 to v4.9] > >>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > >>>> --- > >>> > >>> 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. And needless to say, please test the backported patch before requesting it to be included in stable kernels :-) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
