[U-Boot] ARM: omap3: Implement dpll5 (HSUSB clk) workaround for OMAP36xx/AM/DM37xx according to errata sprz318e.

[Robert Nelson]

On Fri, Aug 16, 2013 at 10:07 AM, Robert Nelson <robertcnelson at gmail.com> wrote:
> On Fri, Aug 16, 2013 at 9:34 AM, Peter A. Bigot <pab at pabigot.com> wrote:
>> On 08/16/2013 08:38 AM, Tom Rini wrote:
>>>
>>> On Wed, Aug 14, 2013 at 09:53:16PM -0500, Peter A. Bigot wrote:
>>>>
>>>> On 07/09/2013 02:43 AM, Naumann Andreas wrote:
>>>>>
>>>>> In chapter 'Advisory 2.1 USB Host Clock Drift Causes USB Spec
>>>>> Non-compliance in Certain Configurations' of the TI Errata it is recommended
>>>>> to use certain div/mult values for the DPLL5 clock setup.
>>>>> So far u-boot used the old 34xx values, so I added the errata
>>>>> recommended values specificly for 36xx init only.
>>>>> Also, the FSEL registers exist no longer, so removed them from init.
>>>>>
>>>>> Tested this on a AM3703 board with 19.2MHz oscillator, which previously
>>>>> couldnt lock the dpll5 (kernel complained). As a consequence the EHCI USB
>>>>> port wasnt usable in U-Boot and kernel. With this patch, kernel panics
>>>>> disappear and USB working fine in u-boot and kernel.
>>>>>
>>>>> Signed-off-by: Andreas Naumann <anaumann at ultratronik.de>
>>>>
>>>> While this patch works with Linux that has been patched for this
>>>> erratum, it will cause problems with some unpatched versions of
>>>> Linux.
>>>
>>> Right.  So Linux also needs to be patched for the erratum.
>>
>>
>> Yes.  My point was that if you update u-boot alone, then try to use it to
>> boot an unpatched Linux that assumes CM_CLKSEL5_PLL has its power-on value,
>> USB will not work.
>>
>> I think it's dangerous to assume that the mixture of an unpatched Linux with
>> a patched u-boot will never occur, and the cause of the failure that results
>> is pretty subtle.  So whatever gets merged would be safer if it restored the
>> default setting of CM_CLKSEL5_PLL prior to handing off control to Linux.
>
> Agree, we should not apply this, till we also have an 'approved' patch
> for mainline linux posted.  Right now we have a set of kernel hacks,
> but no agreed on method as the kernel maintainer did not have a board
> that suffered from the errata..

btw: here's a version that seems to work on v3.11-rc5:

https://raw.github.com/RobertCNelson/armv7-multiplatform/v3.11.x/patches/omap_sprz319_erratum_v2.1/0001-hack-omap-clockk-dpll5-apply-sprz319e-2.1-erratum-kernel-3.11-rc2.patch

Regards,

-- 
Robert Nelson
http://www.rcn-ee.com/