Re: [PATCH for-rc 1/4] IB/hfi1: Allow for all speeds higher than gen3

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On Tue, Oct 29, 2019 at 09:19:34PM +0000, Marciniszyn, Mike wrote:
> > Subject: Re: [PATCH for-rc 1/4] IB/hfi1: Allow for all speeds higher than gen3
> > 
> > On Fri, Oct 25, 2019 at 03:58:24PM -0400, Dennis Dalessandro wrote:
> > > From: James Erwin <james.erwin@xxxxxxxxx>
> > >
> > > The driver avoids the gen3 speed bump when the parent
> > > bus speed isn't identical to gen3, 8.0GT/s.  This is not
> > > compatible with gen4 and newer speeds.
> > >
> > > Fix by relaxing the test to explicitly look for the lower
> > > capability speeds which inherently allows for all future speeds.
> > 
> > This description does not seem like stable material to me.
> > 
> 
> Having a card unknowingly operate at half speed would seem pretty serious to me.

Since gen4 systems are really new this also sounds like a new feature
to me.. You need to be concerned that changing the pci setup doesn't
cause regressions on existing systems too.

> Perhaps the description should say:
> 
> IB/hfi1: Insure full Gen3 speed in a Gen4 system

And maybe explain what the actual user visible impact is here. Sounds
like plugging a card into a gen4 system will not run at gen3 speeds?

Jason



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