[Intel-gfx] [PATCH] drm/i915: Skip DDI PLL selection for DSI

[Ville Syrjälä]

On Tue, Feb 09, 2016 at 01:16:18PM +0530, Thulasimani, Sivakumar wrote:
> 
> 
> On 2/9/2016 12:02 PM, Jani Nikula wrote:
> > On Tue, 09 Feb 2016, "Thulasimani, Sivakumar" <sivakumar.thulasimani at intel.com> wrote:
> >> On 2/5/2016 4:59 PM, Mika Kahola wrote:
> >>> Skip DDI PLL selection if display type is DSI/MIPI.
> >>>
> >>> Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> >>> ---
> >>>    drivers/gpu/drm/i915/intel_display.c | 9 +++++++--
> >>>    1 file changed, 7 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> >>> index d7de2a5..5da98b2 100644
> >>> --- a/drivers/gpu/drm/i915/intel_display.c
> >>> +++ b/drivers/gpu/drm/i915/intel_display.c
> >>> @@ -9902,8 +9902,13 @@ static void broadwell_modeset_commit_cdclk(struct drm_atomic_state *old_state)
> >>>    static int haswell_crtc_compute_clock(struct intel_crtc *crtc,
> >>>    				      struct intel_crtc_state *crtc_state)
> >>>    {
> >>> -	if (!intel_ddi_pll_select(crtc, crtc_state))
> >>> -		return -EINVAL;
> >>> +	struct intel_encoder *intel_encoder =
> >>> +		intel_ddi_get_crtc_new_encoder(crtc_state);
> >>> +
> >>> +	if (intel_encoder->type != INTEL_OUTPUT_DSI) {
> >>> +		if (!intel_ddi_pll_select(crtc, crtc_state))
> >>> +			return -EINVAL;
> >>> +	}
> >>>    
> >> can this be moved inside bxt_ddi_pll_select ? we can avoid this check for
> >> other platforms that also execute this function.
> > I asked Mika to do it this way, but if you feel strongly about it I
> > guess I could be persuaded otherwise too.
> >
> > My main point is, if we pass on DSI encoders to DDI functions in some
> > cases but mostly not, it will muddy the waters and eventually people end
> > up checking for "is dsi" all around DDI just because they can't be
> > bothered to check if the functions are really called for DDI only or
> > not. It's more of a maintainability concern than anything else.
> >
> > BR,
> > Jani.
> >
> i am fine with this either way. i was thinking of avoid such checks
> in other platforms where it is not needed but your concern of
> too many is_dsi checks is valid as well.
> with that i am fine with this change as is.
>   Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani at intel.com>

Another idea would be to use the clock_set thing to skip it, but
I think  historically that has only been used to skip the PLL
calculations, not the PLL selection. So might be it would just confuse
things more.

-- 
Ville Syrjälä
Intel OTC