[PATCH RFC 5/5] ahci_imx: add disable for spread-spectrum

[Russell King - ARM Linux]

On Wed, Apr 16, 2014 at 05:46:47PM -0500, Rob Herring wrote:
> On Wed, Apr 16, 2014 at 3:43 AM, Russell King
> <rmk+kernel at arm.linux.org.uk> wrote:
> > Spread-spectrum doesn't work with Cubox-i hardware, so we have to
> > disable this feature.  Add a DT property so that platforms can
> > indicate that this feature should not be enabled.
> 
> This is for spread-spectrum tx or rx? Transmit SS is optional to
> support, but the receiver must support SS. Otherwise random drives
> won't work which makes for a good user experience. Is this really a
> board quirk rather than a Si issue?

No idea.  This bit controls clock generation, and one reason given to
disable it is if the reference clock being supplied is already spread
spectrum.  I don't think that applies here.  It doesn't say which
clock(s) this is applied to - I would guess it's the transmit clock.

All I know is that with SS enabled, the drive is not detected, and
SolidRun's original port disables SS.  Disabling SS allows the external
drive to be detected.

I have no capability to check the eye pattern, so I've no idea if
there's a problem with the electrical setup which stops SS from
working.  All I know is with the parameters I give here (which are
those which SolidRun's original port uses) and with SS disabled,
it works.

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