Re: [PATCH v2 3/3] drm/amd/display: report synced displays to PowerPlay for MCLK switch

[Richard Lane <richardlanedev@gmail.com>]

On 09/11/2026 20:34, Alex Deucher wrote:
> On Mon, Nov 2, 2026 at 3:31 AM Richard Lane <richardlanedev@gmail.com> wrote:
>>
>> When driving multiple displays or tiled panels with identical timings
>> (such as the two 2560x2880 tiles of an Apple 5K iMac panel), Display
>> Core's program_timing_sync() aligns the CRTCs into a timing sync group
>> in hardware during dc_commit_streams().
>>
>> However, on DCE < 12, Display Core leaves
>> pp_display_cfg.all_displays_in_sync unset. Because PowerPlay is not
>> informed that the streams have synchronized vertical blanking intervals,
>> SMU7 prevents MCLK switching at idle or causes modeset underflows.
>>
>> If all active streams belong to the same timing sync group
>> (timing_sync_info.group_size == params.stream_count), report
>> all_displays_in_sync = true to PowerPlay after committing the streams so
>> SMU7 can safely downclock MCLK at idle.
>>
> 
> Looking at this a little deeper, the function bw_calcs() in
> dce_calcs.c already calculates all_displays_in_sync using the helper
> all_displays_in_sync().  Can you look into this and figure out why
> that is not working as expected?  My concern with this patch is that
> DCE and DCN have different logic for handling mclk switching so I'm
> not sure it's safe to call dm_pp_apply_display_requirements() directly
> from common code.
> 
> Thanks,
> 
> Alex

Moving it to dce_clk_mgr.c and using resource_are_streams_timing_synchronizable() also works. Is that a solution?

diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dce100/dce_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dce100/dce_clk_mgr.c
--- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dce100/dce_clk_mgr.c
+++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dce100/dce_clk_mgr.c
@@ -31,6 +31,7 @@
 #include "dmcu.h"
 #include "core_types.h"
 #include "dal_asic_id.h"
+#include "resource.h"
 
 /*
  * Currently the register shifts and masks in this file are used for dce100 and dce80
@@ -319,8 +320,17 @@ static void dce_pplib_apply_display_requirements(
 	struct dc_state *context)
 {
 	struct dm_pp_display_configuration *pp_display_cfg = &context->pp_display_cfg;
+	int j;
 
 	dce110_fill_display_configs(context, pp_display_cfg);
+	pp_display_cfg->all_displays_in_sync = pp_display_cfg->display_count > 1;
+	for (j = 1; j < context->stream_count; j++) {
+		if (!resource_are_streams_timing_synchronizable(
+			    context->streams[0], context->streams[j])) {
+			pp_display_cfg->all_displays_in_sync = false;
+			break;
+		}
+	}
 
 	if (memcmp(&dc->current_state->pp_display_cfg, pp_display_cfg, sizeof(*pp_display_cfg)) !=  0)
 		dm_pp_apply_display_requirements(dc->ctx, pp_display_cfg);

Richard

> 
>> Signed-off-by: Richard Lane <richardlanedev@gmail.com>
>> ---
>>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> index 74cd88d8d580..b4531383437e 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> @@ -4777,6 +4777,16 @@ static void amdgpu_dm_commit_streams(struct drm_atomic_commit *state,
>>         dc_exit_ips_for_hw_access(dm->dc);
>>         WARN_ON(!dc_commit_streams(dm->dc, &params));
>>
>> +       if (params.stream_count > 1 &&
>> +           dm->dc->current_state->stream_status[0].timing_sync_info.group_size ==
>> +           params.stream_count) {
>> +               struct dm_pp_display_configuration *pp_cfg =
>> +                       &dm->dc->current_state->pp_display_cfg;
>> +
>> +               pp_cfg->all_displays_in_sync = true;
>> +               dm_pp_apply_display_requirements(dm->dc->ctx, pp_cfg);
>> +       }
>> +
>>         bool frl_stream_found = false;
>>
>>         for (i = 0; i < params.stream_count; i++) {
>> --
>> 2.55.0