> -----Original Message-----
> From: Nautiyal, Ankit K <ankit.k.nautiyal@xxxxxxxxx>
> Sent: Sunday, November 1, 2020 3:37 PM
> To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx; Shankar, Uma <uma.shankar@xxxxxxxxx>;
> Kulkarni, Vandita <vandita.kulkarni@xxxxxxxxx>; ville.syrjala@xxxxxxxxxxxxxxx;
> Sharma, Swati2 <swati2.sharma@xxxxxxxxx>
> Subject: [PATCH v2 12/13] drm/i915: Add helper functions for calculating DSC
> parameters for HDMI2.1
>
> The DP-HDMI2.1 PCON spec provides way for a source to set PPS
> parameters: slice height, slice width and bits_per_pixel, based on the HDMI2.1
> sink capabilities. The DSC encoder of the PCON will respect these parameters,
> while preparing the 128 byte PPS.
>
> This patch adds helper functions to calculate these PPS paremeters as per the
> HDMI2.1 specification.
>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_hdmi.c | 181 ++++++++++++++++++++++
> drivers/gpu/drm/i915/display/intel_hdmi.h | 7 +
> 2 files changed, 188 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c
> b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index f90838bc74fb..6b9b9ea7f9b0 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -3438,3 +3438,184 @@ void intel_hdmi_init(struct drm_i915_private
> *dev_priv,
> dig_port->aux_ch = intel_bios_port_aux_ch(dev_priv, port);
> intel_hdmi_init_connector(dig_port, intel_connector); }
> +
> +int intel_hdmi_dsc_get_slice_height(int vactive) {
> + int slice_height;
> +
> + /*
> + * Slice Height determination : HDMI2.1 Section 7.7.5.2
> + * Select smallest slice height >=96, that results in a valid PPS and
> + * requires minimum padding lines required for final slice.
> + *
> + * Assumption : Vactive is even.
> + */
> + for (slice_height = 96; slice_height <= vactive; slice_height += 2)
> + if (vactive % slice_height == 0)
> + return slice_height;
> +
> + return 0;
> +}
> +
> +int
> +intel_hdmi_dsc_get_num_slices(const struct intel_crtc_state *crtc_state,
> + int src_max_slices, int src_max_slice_width,
> + int hdmi_max_slices, int hdmi_throughput) {
It would be good to add a comment describing each of the function parameters, this
will make following code easier.
> +/* Pixel rates in KPixels/sec */
> +#define HDMI_DSC_PEAK_PIXEL_RATE 2720000
> +#define HDMI_DSC_MAX_ENC_THROUGHPUT_0 340000
> +#define HDMI_DSC_MAX_ENC_THROUGHPUT_1 400000
It would be good to add a comment to describe what actually this represent.
> +#define MAX_HDMI_SLICE_WIDTH 2720
How this limit is defined, may be mention of the spec details.
> + int kslice_adjust;
> + int adjusted_clk_khz;
> + int min_slices;
> + int target_slices;
> + int max_throughput; /* max clock freq. in khz per slice */
> + int max_slice_width;
> + int slice_width;
> + int pixel_clock = crtc_state->hw.adjusted_mode.crtc_clock;
> +
> + if (!hdmi_throughput)
> + return 0;
> +
> + /*
> + * Slice Width determination : HDMI2.1 Section 7.7.5.1
> + * kslice_adjust factor for 4:2:0 formats is 0.5, where as
> + * for 4:4:4 is 1.0. Multiplying these factors by 10 and later
> + * dividing adjusted clock value by 10.
> + */
> + if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
> + kslice_adjust = 5;
> + else
> + kslice_adjust = 10;
May be add a note for 422 formats, or fail in that case, not sure if value of 1 holds
good for 422 as well. If it's 1, then ignore the comment.
> +
> + adjusted_clk_khz = DIV_ROUND_UP(kslice_adjust * pixel_clock, 10);
> +
> + if (adjusted_clk_khz <= HDMI_DSC_PEAK_PIXEL_RATE)
> + max_throughput = HDMI_DSC_MAX_ENC_THROUGHPUT_0;
> + else
> + max_throughput = HDMI_DSC_MAX_ENC_THROUGHPUT_1;
A comment describing slight details will be good.
> + /*
> + * Taking into account the sink's capability for maximum
> + * clock per slice (in MHz) as read from HF-VSDB.
> + */
> + max_throughput = min(max_throughput, hdmi_throughput * 1000);
> +
> + if (!max_throughput)
> + return 0;
hdmi_throughput is already checked for 0, so this is not needed.
> + min_slices = DIV_ROUND_UP(adjusted_clk_khz, max_throughput);
> + max_slice_width = min(MAX_HDMI_SLICE_WIDTH, src_max_slice_width);
> +
> + /*
> + * Keep on increasing the num of slices/line, starting from min_slices
> + * per line till we get such a number, for which the slice_width is
> + * just less than max_slice_width. The slices/line selected should be
> + * less than or equal to the max horizontal slices that the combination
> + * of PCON encoder and HDMI decoder can support.
> + */
> + slice_width = max_slice_width;
> +
> + do {
> + if (min_slices <= 1 && src_max_slices >= 1 && hdmi_max_slices
> >= 1)
> + target_slices = 1;
> + else if (min_slices <= 2 && src_max_slices >= 2 &&
> hdmi_max_slices >= 2)
> + target_slices = 2;
> + else if (min_slices <= 4 && src_max_slices >= 4 &&
> hdmi_max_slices >= 4)
> + target_slices = 4;
> + else if (min_slices <= 8 && src_max_slices >= 8 &&
> hdmi_max_slices >= 8)
> + target_slices = 8;
> + else if (min_slices <= 12 && src_max_slices >= 12 &&
> hdmi_max_slices >= 12)
> + target_slices = 12;
> + else if (min_slices <= 16 && src_max_slices >= 16 &&
> hdmi_max_slices >= 16)
> + target_slices = 16;
> + else
> + return 0;
> +
> + slice_width = DIV_ROUND_UP(crtc_state-
> >hw.adjusted_mode.hdisplay, target_slices);
> + if (slice_width >= max_slice_width)
> + min_slices = target_slices + 1;
> + } while (slice_width >= max_slice_width);
> +
> + return target_slices;
> +}
> +
> +int
> +intel_hdmi_dsc_get_bpp(int src_fractional_bpp, int slice_width, int num_slices,
> + int output_format, bool hdmi_all_bpp,
> + int hdmi_max_chunk_bytes)
Describe the parameters here as well.
> +{
> + int max_dsc_bpp, min_dsc_bpp;
> + int target_bytes;
> + bool bpp_found = false;
> + int bpp_decrement_x16;
> + int bpp_target;
> + int bpp_target_x16;
> +
> + /*
> + * Get min bpp and max bpp as per Table 7.23, in HDMI2.1 spec
> + * Start with the max bpp and keep on decrementing with
> + * fractional bpp, if supported by PCON DSC encoder
> + *
> + * for each bpp we check if no of bytes can be supported by HDMI sink
> + */
> +
> + /* Assuming: bpc as 8*/
> + if (output_format == INTEL_OUTPUT_FORMAT_YCBCR420) {
> + min_dsc_bpp = 6;
> + max_dsc_bpp = 3 * 4; /* 3*bpc/2 */
> + } else {
> + min_dsc_bpp = 8;
> + max_dsc_bpp = 3 * 8; /* 3*bpc */
> + }
May be add a note for 422 formats, or fail in that case. I guess 8 and 24 will work
for RGB and 422 will have different values. Please check and fix this.
> +
> + /*
> + * Taking into account if all dsc_all_bpp supported by HDMI2.1 sink
> + * Section 7.7.34 : Source shall not enable compressed Video
> + * Transport with bpp_target settings above 12 bpp unless
> + * DSC_all_bpp is set to 1.
> + */
> + if (!hdmi_all_bpp)
> + max_dsc_bpp = min(max_dsc_bpp, 12);
> +
> + /*
> + * The Sink has a limit of compressed data in bytes for a scanline,
> + * as described in max_chunk_bytes field in HFVSDB block of edid.
> + * The no. of bytes depend on the target bits per pixel that the
> + * source configures. So we start with the max_bpp and calculate
> + * the target_chunk_bytes. We keep on decrementing the target_bpp,
> + * till we get the target_chunk_bytes just less than what the sink's
> + * max_chunk_bytes, or else till we reach the min_dsc_bpp.
> + *
> + * The decrement is according to the fractional support from PCON DSC
> + * encoder. For fractional BPP we use bpp_target as a multiple of 16.
> + *
> + * bpp_target_x16 = bpp_target * 16
> + * So we need to decrement by {1, 2, 4, 8, 16} for fractional bpps
> + * {1/16, 1/8, 1/4, 1/2, 1} respectively.
> + */
> +
> + bpp_target = max_dsc_bpp;
> + if (src_fractional_bpp)
I think you missed a ! here
> + return 0;
> + bpp_decrement_x16 = DIV_ROUND_UP(16, src_fractional_bpp);
> + bpp_target_x16 = (bpp_target * 16) - bpp_decrement_x16;
> +
> + while (bpp_target_x16 > (min_dsc_bpp * 16)) {
> + int bpp;
> +
> + bpp = DIV_ROUND_UP(bpp_target_x16, 16);
> + target_bytes = num_slices * slice_width * DIV_ROUND_UP(bpp,
> 8);
> + if (target_bytes <= hdmi_max_chunk_bytes) {
> + bpp_found = true;
> + break;
> + }
> + bpp_target_x16 -= bpp_decrement_x16;
Not sure on the overall calculation on this part, but if this works then I am good. Please confirm the
same with actual bpp values computed and validate.
> + }
> + if (bpp_found)
> + return bpp_target_x16;
I think we should divide by 16 and return. Isn't it ?
> +
> + return 0;
> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.h
> b/drivers/gpu/drm/i915/display/intel_hdmi.h
> index 15eb0ccde76e..fa1a9b030850 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.h
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.h
> @@ -50,5 +50,12 @@ bool intel_hdmi_limited_color_range(const struct
> intel_crtc_state *crtc_state,
> const struct drm_connector_state
> *conn_state); bool intel_hdmi_deep_color_possible(const struct intel_crtc_state
> *crtc_state, int bpc,
> bool has_hdmi_sink, bool ycbcr420_output);
> +int intel_hdmi_dsc_get_bpp(int src_fractional_bpp, int slice_width,
> + int num_slices, int output_format, bool hdmi_all_bpp,
> + int hdmi_max_chunk_bytes);
> +int intel_hdmi_dsc_get_num_slices(const struct intel_crtc_state *crtc_state,
> + int src_max_slices, int src_max_slice_width,
> + int hdmi_max_slices, int hdmi_throughput); int
> +intel_hdmi_dsc_get_slice_height(int vactive);
>
> #endif /* __INTEL_HDMI_H__ */
> --
> 2.17.1
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