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SubjectRe: [PATCH 2/2] spi: Add Qualcomm QUP SPI controller support
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Date

Hi,

On Mon, 2014-02-10 at 12:29 -0800, Courtney Cavin wrote:
> On Mon, Feb 10, 2014 at 08:41:44PM +0100, Ivan T. Ivanov wrote:
> >
> > Hi,
> >
> > On Mon, 2014-02-10 at 11:47 -0600, Andy Gross wrote:
> > > On Mon, Feb 10, 2014 at 06:55:02PM +0200, Ivan T. Ivanov wrote:
> > >
> > > [....]
> > >
> > > > > > > Bail here?
> > > > > >
> > > > > > I don't know. What will be the consequences if controller continue to
> > > > > > operate on its default rate?
> > > > > >
> > > > >
> > > > > It is unclear. But if you can't set the rate that is configured or if there is
> > > > > a misconfiguration, it's probably better to exit the probe and catch it here.
> > > >
> > > >
> > > > My preference is to delay clock speed change till first
> > > > SPI transfer. And use wherever transfer itself mandate.
> > > >
> > >
> > > That works. My only concern is that it might be nice to catch a configuration
> > > problem early rather than wait for the SPI transfer to fail continuously.
> >
> > If developer is skilled enough to know which version controller is,
> > (s)he will be able to put the right frequency constrain here :-)
>
> A developer doesn't have to have much skill at all to copy-paste DT
> configurations around and muck with numbers.... I agree with Andy here,
> early validation is a good idea here, at the very least, some sanity
> checks.

Actually, thinking more on this. Supplying SPI controller with,
let say 50MHz, which is what success of clk_set_rate() means, doesn't
necessarily guaranteer that controller will be able to do transfers
properly, right? Setting frequency at this point didn't bring any
benefit.

Regards,
Ivan


>
> -Courtney




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