[PATCH 1/9] drm: Add helpers for x16 fixed point values

[Imre Deak]

On Wed, Jun 19, 2024 at 01:10:09PM +0300, Jani Nikula wrote:
> On Fri, 14 Jun 2024, Imre Deak <imre.deak at intel.com> wrote:
> > Add helpers to convert between x16 fixed point and integer/fraction
> > values. Also add the format/argument macros required to printk x16
> > fixed point variables.
> >
> > These are needed by later patches dumping the Display Stream Compression
> > configuration in DRM core and in the i915 driver to replace the
> > corresponding bpp_x16 helpers defined locally in the driver.
> >
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/display/drm_dp_helper.c |  5 +++--
> >  include/drm/drm_fixed.h                 | 23 +++++++++++++++++++++++
> >  2 files changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> > index 79a615667aab1..806f9c9764995 100644
> > --- a/drivers/gpu/drm/display/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> > @@ -35,6 +35,7 @@
> >  #include <drm/display/drm_dp_helper.h>
> >  #include <drm/display/drm_dp_mst_helper.h>
> >  #include <drm/drm_edid.h>
> > +#include <drm/drm_fixed.h>
> >  #include <drm/drm_print.h>
> >  #include <drm/drm_vblank.h>
> >  #include <drm/drm_panel.h>
> > @@ -4151,9 +4152,9 @@ int drm_dp_bw_overhead(int lane_count, int hactive,
> >  	int symbol_cycles;
> >  
> >  	if (lane_count == 0 || hactive == 0 || bpp_x16 == 0) {
> > -		DRM_DEBUG_KMS("Invalid BW overhead params: lane_count %d, hactive %d, bpp_x16 %d.%04d\n",
> > +		DRM_DEBUG_KMS("Invalid BW overhead params: lane_count %d, hactive %d, bpp_x16 " DRM_X16_FMT "\n",
> >  			      lane_count, hactive,
> > -			      bpp_x16 >> 4, (bpp_x16 & 0xf) * 625);
> > +			      DRM_X16_ARGS(bpp_x16));
> >  		return 0;
> >  	}
> >  
> > diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
> > index 81572d32db0c2..0fe2a7f50d54e 100644
> > --- a/include/drm/drm_fixed.h
> > +++ b/include/drm/drm_fixed.h
> > @@ -214,4 +214,27 @@ static inline s64 drm_fixp_exp(s64 x)
> >  	return sum;
> >  }
> >  
> > +static inline int drm_x16_from_int(int val_int)
> > +{
> > +	return val_int << 4;
> > +}
> > +
> > +static inline int drm_x16_to_int(int val_x16)
> > +{
> > +	return val_x16 >> 4;
> > +}
> > +
> > +static inline int drm_x16_to_int_roundup(int val_x16)
> > +{
> > +	return (val_x16 + 0xf) >> 4;
> > +}
> > +
> > +static inline int drm_x16_to_frac(int val_x16)
> > +{
> > +	return val_x16 & 0xf;
> > +}
> 
> Sad trombone about the completely different naming scheme compared to
> the rest of the file.
> 
> Not saying the existing naming is great, but neither is this. And
> there's no way to unify except by renaming *both* afterwards.
> 
> We could devise a scheme now that could be used for the existing stuff
> later, without renaming the new stuff.

Based on [1]'s short variant, we could have:

dfixed*(fixed20_12 v)  -> drm_uq12*(drm_uq20_12_t v)
drm_fixp*(s64 v)       -> drm_q32*(s64 v)
drm_x16*(int v)        -> drm_q4*(int v)

Or instead of uq12/q32/q4 using ufp12/fp32/fp4.

[1] https://en.wikipedia.org/wiki/Q_(number_format)

> *shrug*
> 
> BR,
> Jani.
> 
> 
> 
> > +
> > +#define DRM_X16_FMT		"%d.%04d"
> > +#define DRM_X16_ARGS(val_x16)	drm_x16_to_int(val_x16), (drm_x16_to_frac(val_x16) * 625)
> > +
> >  #endif
> 
> -- 
> Jani Nikula, Intel