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

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 4/28/2025 7:01 PM, 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@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 */

Makes sense, I can take this up later.

Patch LGTM.

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

>   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;