Some nitpicks below
On Tue, 2019-08-20 at 15:11 -0400, David Francis wrote:
> We were using drm helpers to convert a timing into its
> bandwidth, its bandwidth into pbn, and its pbn into timeslots
>
> These helpers
> -Did not take DSC timings into account
> -Used the link rate and lane count of the link's aux device,
> which are not the same as the link's current cap
> -Did not take FEC into account (FEC reduces the PBN per timeslot)
>
> For converting timing into PBN, add a new function
> drm_dp_calc_pbn_mode_dsc that handles the DSC case
>
> For converting PBN into time slots, amdgpu doesn't use the
> 'correct' atomic method (drm_dp_atomic_find_vcpi_slots), so
> don't add a new helper to cover our approach. Use the same
> means of calculating pbn per time slot as the DSC code.
>
> v2: Add drm helper for clock to pbn conversion
>
> Cc: Jerry Zuo <Jerry.Zuo@xxxxxxx>
> Cc: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
> Signed-off-by: David Francis <David.Francis@xxxxxxx>
> ---
> .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 18 +++++---
> drivers/gpu/drm/drm_dp_mst_topology.c | 41 +++++++++++++++++++
> include/drm/drm_dp_mst_helper.h | 2 +-
> 3 files changed, 54 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> index 5f2c315b18ba..dfa99e0d6e64 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> @@ -189,8 +189,8 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
> int slots = 0;
> bool ret;
> int clock;
> - int bpp = 0;
> int pbn = 0;
> + int pbn_per_timeslot, bpp = 0;
>
> aconnector = (struct amdgpu_dm_connector *)stream->dm_stream_context;
>
> @@ -208,7 +208,6 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
> clock = stream->timing.pix_clk_100hz / 10;
>
> switch (stream->timing.display_color_depth) {
> -
> case COLOR_DEPTH_666:
> bpp = 6;
> break;
> @@ -234,11 +233,18 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
>
> bpp = bpp * 3;
>
> - /* TODO need to know link rate */
> -
> - pbn = drm_dp_calc_pbn_mode(clock, bpp);
> +#ifdef CONFIG_DRM_AMD_DC_DSC_SUPPORT
> + if (stream->timing.flags.DSC)
> + pbn = drm_dp_calc_pbn_mode_dsc(clock,
> + stream-
> >timing.dsc_cfg.bits_per_pixel);
> + else
> +#endif
> + pbn = drm_dp_calc_pbn_mode(clock, bpp);
>
> - slots = drm_dp_find_vcpi_slots(mst_mgr, pbn);
> + /* Convert kilobits per second / 64 (for 64 timeslots) to pbn
> (54/64 megabytes per second) */
> + pbn_per_timeslot = dc_link_bandwidth_kbps(
> + stream->link, dc_link_get_link_cap(stream-
> >link)) / (8 * 1000 * 54);
> + slots = DIV_ROUND_UP(pbn, pbn_per_timeslot);
> ret = drm_dp_mst_allocate_vcpi(mst_mgr, mst_port, pbn, slots);
>
> if (!ret)
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 398e7314ea8b..d789b7af7dbf 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3588,6 +3588,47 @@ static int test_calc_pbn_mode(void)
> return 0;
> }
>
> +/**
> + * drm_dp_calc_pbn_mode_dsc() - Calculate the PBN for a mode with DSC
> enabled.
> + * @clock: dot clock for the mode
> + * @dsc_bpp: dsc bits per pixel x16 (e.g. dsc_bpp = 136 is 8.5 bpp)
> + *
> + * This uses the formula in the spec to calculate the PBN value for a mode,
> + * given that the mode is using DSC
You should use the proper kdoc formatting for documenting return values (not
all of the DP MST code does this currently, but that's a bug I haven't taken
the time to fix :):
/*
* foo_bar() - foo the bar
*
* foos the bar, guaranteed
* Returns:
* Some magic number
*/
> + */
> +int drm_dp_calc_pbn_mode_dsc(int clock, int dsc_bpp)
> +{
> + u64 kbps;
> + s64 peak_kbps;
> + u32 numerator;
> + u32 denominator;
> +
> + kbps = clock * dsc_bpp;
> +
> + /*
> + * margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
> + * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
> + * common multiplier to render an integer PBN for all link rate/lane
> + * counts combinations
> + * calculate
> + * peak_kbps *= (1/16) bppx16 to bpp
> + * peak_kbps *= (1006/1000)
> + * peak_kbps *= (64/54)
> + * peak_kbps *= 8 convert to bytes
> + *
> + * Divide numerator and denominator by 16 to avoid overflow
> + */
> +
> + numerator = 64 * 1006 / 16;
> + denominator = 54 * 8 * 1000 * 1000;
> +
> + kbps *= numerator;
> + peak_kbps = drm_fixp_from_fraction(kbps, denominator);
> +
> + return drm_fixp2int_ceil(peak_kbps);
> +}
> +EXPORT_SYMBOL(drm_dp_calc_pbn_mode_dsc);
> +
> /* we want to kick the TX after we've ack the up/down IRQs. */
> static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr)
> {
> diff --git a/include/drm/drm_dp_mst_helper.h
> b/include/drm/drm_dp_mst_helper.h
> index 2ba6253ea6d3..ddb518f2157a 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -611,7 +611,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector
> *connector, struct drm_dp_
>
>
> int drm_dp_calc_pbn_mode(int clock, int bpp);
> -
> +int drm_dp_calc_pbn_mode_dsc(int clock, int dsc_bpp);
>
> bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
> struct drm_dp_mst_port *port, int pbn, int
> slots);
--
Cheers,
Lyude Paul
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