On Tue, 2017-04-04 at 11:40 +0300, Jani Nikula wrote:
> On Tue, 04 Apr 2017, Ander Conselvan De Oliveira <conselvan2@xxxxxxxxx> wrote:
> > On Tue, 2017-04-04 at 11:15 +0300, Jani Nikula wrote:
> > > From: Madhav Chauhan <madhav.chauhan@xxxxxxxxx>
> > >
> > > As per BSPEC, valid cdclk values for glk are 79.2, 158.4, 316.8 Mhz.
> > > Practically we can achive only 99% of these cdclk values (HW team
> > > checking on this). So cdclk should be calculated for the given pixclk as
> > > per that otherwise it may lead to screen corruption for some scenarios.
> > >
> > > v2: Rebased to new CDLCK code framework
> > > v3: Addressed review comments from Ander/Jani
> > > - Add comment in code about 99% usage of CDCLK
> > > - Calculate max dot clock as well with 99% limit
> > > v4 by Jani:
> > > - drop superfluous whitespace change
> > > - rewrite code comments to clarify
> > >
> > > Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@xxxxxxxxx>
> > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Madhav Chauhan <madhav.chauhan@xxxxxxxxx>
> > > Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> > > ---
> > > drivers/gpu/drm/i915/intel_cdclk.c | 16 +++++++++++++---
> > > 1 file changed, 13 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
> > > index dd3ad52b7dfe..763010f8ad89 100644
> > > --- a/drivers/gpu/drm/i915/intel_cdclk.c
> > > +++ b/drivers/gpu/drm/i915/intel_cdclk.c
> > > @@ -1071,9 +1071,15 @@ static int bxt_calc_cdclk(int max_pixclk)
> > >
> > > static int glk_calc_cdclk(int max_pixclk)
> > > {
> > > - if (max_pixclk > 2 * 158400)
> > > + /*
> > > + * FIXME: Avoid using a pixel clock that is more than 99% of the cdclk
> > > + * as a temporary workaround. Use a higher cdclk instead. (Note that
> >
> > Temporary workaround for what? Neither the comment nor the commit message
> > explicitly lists the scenario that triggers this issue.
>
> Frankly I did not know what to write.
> There are issues with pixel clocks
> near cdclk that shouldn't happen. People are looking into this, but in
> the mean time dodge the issues by using higher cdclk. The issue should
> not be encoder specific, but in practice this has only been seen with
> DSI because there were some modes with pixel clocks that are near the
> cdclk.
The above plus the model number of the DSI panel with which the issue has been
seen would be good enough IMO.
Ander
> > With that fixed,
> >
> > Reviewed-by: Ander Conselvan de Oliveira <conselvan2@xxxxxxxxx>
> >
> > > + * intel_compute_max_dotclk() limits the max pixel clock to 99% of max
> > > + * cdclk.)
> > > + */
> > > + if (max_pixclk > DIV_ROUND_UP(2 * 158400 * 99, 100))
> > > return 316800;
> > > - else if (max_pixclk > 2 * 79200)
> > > + else if (max_pixclk > DIV_ROUND_UP(2 * 79200 * 99, 100))
> > > return 158400;
> > > else
> > > return 79200;
> > > @@ -1664,7 +1670,11 @@ static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv)
> > > int max_cdclk_freq = dev_priv->max_cdclk_freq;
> > >
> > > if (IS_GEMINILAKE(dev_priv))
> > > - return 2 * max_cdclk_freq;
> > > + /*
> > > + * FIXME: Limiting to 99% as a temporary workaround. See
> > > + * glk_calc_cdclk() for details.
> > > + */
> > > + return 2 * max_cdclk_freq * 99 / 100;
> > > else if (INTEL_INFO(dev_priv)->gen >= 9 ||
> > > IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
> > > return max_cdclk_freq;
>
>
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