On Tue, Jan 3, 2017 at 4:16 PM, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > 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 :-) > Tested against linux-stable 4.4.y branch, linux-stable-4.8.y branch, and 4.9.0 :-) > -- > 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
