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

[Peter A. Bigot <pab@pabigot.com>]

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@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.

Peter