> -----Original Message----- > From: Ander Conselvan De Oliveira [mailto:conselvan2@xxxxxxxxx] > Sent: Tuesday, April 4, 2017 4:13 PM > To: Chauhan, Madhav <madhav.chauhan@xxxxxxxxx>; Nikula, Jani > <jani.nikula@xxxxxxxxx>; intel-gfx@xxxxxxxxxxxxxxxxxxxxx > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > Subject: Re: [PATCH] drm/i915/glk: limit pixel clock to 99% of cdclk > workaround > > On Tue, 2017-04-04 at 10:27 +0000, Chauhan, Madhav wrote: > > > -----Original Message----- > > > From: Nikula, Jani > > > Sent: Tuesday, April 4, 2017 3:48 PM > > > To: Ander Conselvan De Oliveira <conselvan2@xxxxxxxxx>; intel- > > > gfx@xxxxxxxxxxxxxxxxxxxxx > > > Cc: Chauhan, Madhav <madhav.chauhan@xxxxxxxxx>; Ville Syrjälä > > > <ville.syrjala@xxxxxxxxxxxxxxx> > > > Subject: Re: [PATCH] drm/i915/glk: limit pixel clock to 99% of cdclk > > > workaround > > > > > > On Tue, 04 Apr 2017, Ander Conselvan De Oliveira > > > <conselvan2@xxxxxxxxx> > > > wrote: > > > > 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. > > > > > > Madhav? > > > > Issue is generic (valid for DP/HDMI) not just MIPI DSI specific. > > Particular DSI panel exposing this issue as described below: > > 1. For XXXX panel (19X12) required pixclk is 157100 KHZ 2. > > glk_calc_cdclk returns 79200 KHZ for this pixclk. For 2PPC it will be > > 158400 KHZ 3. Practically 100% of the cdclk can’t be achieved, so 99% of > 158400 KHZ = 156816 which is less than the desired pixlclk. > > This causes the corruption. > > > > So why do we need to mention a particular panel?? > > If someone else needs to deal with this six months or a year from now and > you, me and Jani are nowhere to be found, the code or commit message > should still have enough information to let that person assess whether it is > safe to remove the workaround or not. Having the model number just makes > it easier to determine what real world scenario triggers this problem, so it is > easier to test a fix. Agree from this perspective. Will add this explanation in commit message. > > Ander > > > > > > > > > > > > > > > > > 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; > > > > > > > > > > > > > > > > -- > > > Jani Nikula, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
