[PATCH v2 06/14] drm/dp-mst: Use dc and drm helpers to compute timeslots

[Kazlauskas, Nicholas]

On 8/20/19 4:43 PM, Lyude Paul wrote:
> 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 at amd.com>
>> Cc: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>> Signed-off-by: David Francis <David.Francis at amd.com>

I would like ot see Lyude's nitpicks addressed but also having this 
patch split into one that just adds the helper and another that uses it 
in amdgpu.

Nicholas Kazlauskas

>> ---
>>   .../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);