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

[Imre Deak]

On Wed, Jun 19, 2024 at 03:01:03PM +0300, Imre Deak wrote:
> 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.

Jani, any objection to using the drm_fp4_from_int() etc. names?

> [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