[Intel-gfx] [PATCH 2/3] drm/i915: add lpt_init_pch_refclk

[Daniel Vetter]

On Sun, Dec 09, 2012 at 07:35:13PM -0200, Paulo Zanoni wrote:
> Hi
> 
> 2012/12/8 Damien Lespiau <damien.lespiau at intel.com>:
> > On Sat, Dec 1, 2012 at 2:04 PM, Paulo Zanoni <przanoni at gmail.com> wrote:
> >> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >>
> >> We need this code to init the PCH SSC refclk and the FDI registers.
> >> The BIOS does this too and that's why VGA worked before this patch,
> >> until you tried to suspend the machine...
> >>
> >> This patch implements the "Sequence to enable CLKOUT_DP for FDI usage
> >> and configure PCH FDI/IO" from our documentation.
> >>
> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >
> >> +       if (IS_HASWELL(dev) && (dev->pci_device & 0xFF00) == 0x0C00)
> >> +               is_sdv = true;
> >
> > Maybe have a IS_SDV() or IS_HSW_SDV() macro like we have a IS_ULT()
> > one? The check should be on the PCH revision but hopefully there's a
> > 1:1 correlation?
> 
> We should just remove this code in the future, maybe even now... I did
> not care too much about creating a macro since this is going to be
> killed.

Added a comment to remind us of that.

> >
> >> +               if (wait_for_atomic_us(I915_READ(SOUTH_CHICKEN2) &
> >> +                                      FDI_MPHY_IOSFSB_RESET_STATUS, 100))
> >> +                       DRM_ERROR("FDI mPHY resert assert timeout\n");
> >
> > s/resert/reset/
> >
> >> +
> >> +               tmp = I915_READ(SOUTH_CHICKEN2);
> >> +               tmp &= ~FDI_MPHY_IOSFSB_RESET_CTL;
> >> +               I915_WRITE(SOUTH_CHICKEN2, tmp);
> >> +
> >> +               if (wait_for_atomic_us((I915_READ(SOUTH_CHICKEN2) &
> >> +                                       FDI_MPHY_IOSFSB_RESET_STATUS) == 0,
> >> +                                      100))
> >> +                       DRM_ERROR("FDI mPHY reset de-assert timeout\n");
> >> +       }
> >
> > When either of those two waits error out, we carry on the sequence. We
> > should probably fail and disable the VGA output (one of those error
> > paths that never get to be tested, yey! I don't know how well we
> > support connectors disappearing)?
> 
> We have this "pattern" in many places: the doc tells us "wait for this
> bit or wait at least XXXms", then we wait using wait_for and print
> DRM_ERROR in case we timeout. In theory, even if we hit the timeout,
> we should be fine since we've already waited for the amount of time
> the spec tells us to wait... I'm not really sure what's the best thing
> to do here, but it really seems we're probably never hit the "fail"
> path.

Imo this is ok. If the hw is in a non-cooperative mood, there's not much
we can do than detect it and hope for the best.

> >> +       tmp = intel_sbi_read(dev_priv, SBI_DBUFF0, SBI_ICLK);
> >> +       tmp |= SBI_DBUFF0_ENABLE;
> >> +       intel_sbi_write(dev_priv, SBI_DBUFF0, tmp, SBI_ICLK);
> >
> > Th ULT path is missing there.
> 
> The ULT will never reach this point, there's not VGA.

Added a comment.

Another bikeshed: Can we have less magic here, or are the docs as opaque
as the code here? I've merged it for now, but usually Dave' doesn't like
this much magic in the code, so a fixup patch would be nice. Imo just
giving the register some names should be good enough.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch