[PATCH v2 07/12] drm/i915/dp: Limit max link bpp properly to a fractional value on SST

[Luca Coelho]

On Mon, 2025-04-28 at 16:31 +0300, Imre Deak wrote:
> The maximum link bpp - determined by the link BW for instance - can be
> fractional, handle this properly during computing the link bpp on SST.
> 
> This keeps the pipe joiner specific maximum link bpp as a rounded-down
> integer value still, changing that to a fractional value is left for
> later.
> 
> v2: Align the min/max bpp value to the bpp step.
> 
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 42b45598a0134..7abc5286f4ccc 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -27,6 +27,8 @@
>  
>  #include <linux/export.h>
>  #include <linux/i2c.h>
> +#include <linux/log2.h>
> +#include <linux/math.h>
>  #include <linux/notifier.h>
>  #include <linux/seq_buf.h>
>  #include <linux/slab.h>
> @@ -938,6 +940,7 @@ static u32 ultrajoiner_ram_max_bpp(u32 mode_hdisplay)
>  	return ultrajoiner_ram_bits() / mode_hdisplay;
>  }
>  
> +/* TODO: return a bpp_x16 value */
>  static
>  u32 get_max_compressed_bpp_with_joiner(struct intel_display *display,
>  				       u32 mode_clock, u32 mode_hdisplay,
> @@ -2152,24 +2155,16 @@ static int dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
>  	const struct intel_connector *connector = to_intel_connector(conn_state->connector);
>  	const struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
>  	int output_bpp;
> -	int dsc_min_bpp;
> -	int dsc_max_bpp;
>  	int min_bpp_x16, max_bpp_x16, bpp_step_x16;
>  	int dsc_joiner_max_bpp;
>  	int num_joined_pipes = intel_crtc_num_joined_pipes(pipe_config);
>  	int bpp_x16;
>  	int ret;
>  
> -	dsc_min_bpp = fxp_q4_to_int_roundup(limits->link.min_bpp_x16);
> -
>  	dsc_joiner_max_bpp = get_max_compressed_bpp_with_joiner(display, adjusted_mode->clock,
>  								adjusted_mode->hdisplay,
>  								num_joined_pipes);
> -	dsc_max_bpp = min(dsc_joiner_max_bpp, fxp_q4_to_int(limits->link.max_bpp_x16));
> -
> -	/* FIXME: remove the round trip via integers */
> -	min_bpp_x16 = fxp_q4_from_int(dsc_min_bpp);
> -	max_bpp_x16 = fxp_q4_from_int(dsc_max_bpp);
> +	max_bpp_x16 = min(fxp_q4_from_int(dsc_joiner_max_bpp), limits->link.max_bpp_x16);
>  
>  	bpp_step_x16 = intel_dp_dsc_bpp_step_x16(connector);
>  
> @@ -2177,6 +2172,10 @@ static int dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
>  	output_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);
>  	max_bpp_x16 = min(max_bpp_x16, fxp_q4_from_int(output_bpp) - bpp_step_x16);
>  
> +	drm_WARN_ON(display->drm, !is_power_of_2(bpp_step_x16));
> +	min_bpp_x16 = round_up(limits->link.min_bpp_x16, bpp_step_x16);
> +	max_bpp_x16 = round_down(max_bpp_x16, bpp_step_x16);
> +
>  	for (bpp_x16 = max_bpp_x16; bpp_x16 >= min_bpp_x16; bpp_x16 -= bpp_step_x16) {
>  		if (!intel_dp_dsc_valid_compressed_bpp(intel_dp, bpp_x16))
>  			continue;

Reviewed-by: Luca Coelho <luciano.coelho at intel.com>

--
Cheers,
Luca.