Re: Initial signal voltage ?

[Joakim Tjernlund <joakim.tjernlund@transmode.se>]

On Thu, 2015-08-27 at 16:44 +0200, Ulf Hansson wrote:
> [...]
> 
> > > 
> > > Currently drivers return error codes according to when they can't set
> > > the requested voltage level, so that's all fine - right?
> > 
> > Yes, they should. Hovever it seems like my fsl controller cannot.
> > There is VS18,VS30 and VS33 bits in hostcap register but theses are
> > always set :(
> 
> If there are set in the *hostcap* register, doesn't that indicates
> that they are supported? Not what's currently used!?

hmm, this only shows that I am a newbie in this area :)
What register/bits normally holds this info?
> 
> What controller/driver are you using here?

esdhc,v3.0/sdhci-of-esdhc


> > > Moreover, the above code snippet is modified by you (or someone else)
> > > locally, since in the upstream version of the code, the prints are
> > 
> > ahh, yes a did that while debugging.
> > 
> > > done a debug level. That's also okay, I think.
> > > Perhaps changing the last print to warn level instead, since reaching
> > > that point would mean all attempts have failed.
> > 
> > Since not all controllers can tell what VS is you have to specify that, in my case I
> > do it in my device tree as there is a way to do that already.
> > 
> > So I think mmc_power_up() should mask away VS not supported and then try the remaining.
> > The exact way to do this escapes me as I am not familiar with this area yet.
> 
> Okay, I think we could potentially look at the host caps and figure
> out what IO voltage level the host supports before trying to set them.
> 
> Although it does complicates things, so before going there I just want
> to be sure that we really have an issue here.
> 
> I haven't yet really understood why your driver is unable to return
> error codes when failing to set an unsupported voltage level, you need
> to convince me on that.

None the less, the info is there in the host caps so why not use it?
If caps say 1.8V only why insist on trying 3/3.3 Volt?

 Jocke