Re: [PATCH v3 16/19] drm/amd/display: Add parameter to control ALLM behavior

["Tomasz Pakuła" <tomasz.pakula.oficjalny@gmail.com>]

On Fri, 2026-02-06 at 13:52 -0500, Harry Wentland wrote:
> On 2026-02-03 13:56, Tomasz Pakuła wrote:
> > [Why]
> > Some users prefer to always manually control ALLM/Gaming mode while
> > others might want it permanently forced on.
> > 
> > [How]
> > Since there isn't yet an API to control this, expose module parameter
> > 
> > Changes in v3:
> > - Include a fix for possible NULL pointer dereference by Peter
> > 
> > Closes: https://github.com/CachyOS/linux-cachyos/issues/680
> > 
> > Co-developed-by: Peter Jung <admin@ptr1337.dev>
> > Signed-off-by: Peter Jung <admin@ptr1337.dev>
> > Signed-off-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.com>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/amdgpu.h           |  1 +
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       | 14 +++++-
> >  .../gpu/drm/amd/display/dc/core/dc_resource.c |  7 +--
> >  .../amd/display/modules/inc/mod_info_packet.h |  1 +
> >  .../display/modules/info_packet/info_packet.c | 46 ++++++++++++++++---
> >  5 files changed, 56 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > index 447e734c362b..312aa32064d5 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > @@ -268,6 +268,7 @@ extern int amdgpu_rebar;
> >  
> >  extern int amdgpu_wbrf;
> >  extern int amdgpu_user_queue;
> > +extern uint amdgpu_allm_mode;
> >  
> >  extern uint amdgpu_hdmi_hpd_debounce_delay_ms;
> >  
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > index d6d0a6e34c6b..4b038c8bbf9f 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > @@ -248,6 +248,7 @@ int amdgpu_umsch_mm_fwlog;
> >  int amdgpu_rebar = -1; /* auto */
> >  int amdgpu_user_queue = -1;
> >  uint amdgpu_hdmi_hpd_debounce_delay_ms;
> > +uint amdgpu_allm_mode = 1;
> >  
> >  DECLARE_DYNDBG_CLASSMAP(drm_debug_classes, DD_CLASS_TYPE_DISJOINT_BITS, 0,
> >  			"DRM_UT_CORE",
> > @@ -1124,7 +1125,7 @@ module_param_named(rebar, amdgpu_rebar, int, 0444);
> >  MODULE_PARM_DESC(user_queue, "Enable user queues (-1 = auto (default), 0 = disable, 1 = enable, 2 = enable UQs and disable KQs)");
> >  module_param_named(user_queue, amdgpu_user_queue, int, 0444);
> >  
> > -/*
> > +/**
> >   * DOC: hdmi_hpd_debounce_delay_ms (uint)
> >   * HDMI HPD disconnect debounce delay in milliseconds.
> >   *
> > @@ -1134,6 +1135,17 @@ module_param_named(user_queue, amdgpu_user_queue, int, 0444);
> >  MODULE_PARM_DESC(hdmi_hpd_debounce_delay_ms, "HDMI HPD disconnect debounce delay in milliseconds (0 to disable (by default), 1500 is common)");
> >  module_param_named(hdmi_hpd_debounce_delay_ms, amdgpu_hdmi_hpd_debounce_delay_ms, uint, 0644);
> >  
> > +/**
> > + * DOC: allm_mode (int)
> > + * Changes ALLM triggering mode (if sink supports ALLM). Possible values:
> > + *
> > + * - 0 = ALLM disabled
> > + * - 1 = ALLM dynamically triggered based on VRR state / Game Content Type Hint
> > + * - 2 = ALLM forced always on
> > + */
> > +MODULE_PARM_DESC(allm_mode, "Changes ALLM trigger mode (0 = disable, 1 = enable (default), 2 = force enable)");
> > +module_param_named(allm_mode, amdgpu_allm_mode, uint, 0644);
> > +
> >  /* These devices are not supported by amdgpu.
> >   * They are supported by the mach64, r128, radeon drivers
> >   */
> > diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > index 4a7c9f810e35..b779aac28dfa 100644
> > --- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > +++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > @@ -44,6 +44,7 @@
> >  #include "clk_mgr.h"
> >  #include "dc_state_priv.h"
> >  #include "dc_stream_priv.h"
> > +#include "modules/inc/mod_info_packet.h"
> 
> Architecturally DC can't have a dependency on modules.
> Is there a different way we can handle this?
> 
> Could we do the determination in amdgpu_dm (with help of
> the module) and then set a flag on the stream?
> 
> Harry

Sure. I don't have any opinion on how it should be done. I think I only
did this like that because I wanted it to be easily changeable at
runtime, but the value of having this RW is next to none.

> 
> >  
> >  #include "virtual/virtual_link_hwss.h"
> >  #include "link/hwss/link_hwss_dio.h"
> > @@ -4503,8 +4504,6 @@ static void set_avi_info_frame(
> >  	unsigned int vic = pipe_ctx->stream->timing.vic;
> >  	unsigned int rid = pipe_ctx->stream->timing.rid;
> >  	unsigned int fr_ind = pipe_ctx->stream->timing.fr_index;
> > -	enum dc_timing_3d_format format;
> > -	bool allm;
> >  
> >  	if (stream->avi_infopacket.valid) {
> >  		*info_packet = stream->avi_infopacket;
> > @@ -4658,10 +4657,8 @@ static void set_avi_info_frame(
> >  	///VIC
> >  	if (pipe_ctx->stream->timing.hdmi_vic != 0)
> >  		vic = 0;
> > -	format = stream->timing.timing_3d_format;
> > -	allm = stream->link->local_sink->edid_caps.allm;
> >  	/*todo, add 3DStereo support*/
> > -	if ((format != TIMING_3D_FORMAT_NONE) || allm) {
> > +	if (!is_hdmi_vic_mode(pipe_ctx->stream)) {
> >  		// Based on HDMI specs hdmi vic needs to be converted to cea vic when 3D is enabled
> >  		switch (pipe_ctx->stream->timing.hdmi_vic) {
> >  		case 1:
> > diff --git a/drivers/gpu/drm/amd/display/modules/inc/mod_info_packet.h b/drivers/gpu/drm/amd/display/modules/inc/mod_info_packet.h
> > index 306eb7355c25..9ec123ecc7c4 100644
> > --- a/drivers/gpu/drm/amd/display/modules/inc/mod_info_packet.h
> > +++ b/drivers/gpu/drm/amd/display/modules/inc/mod_info_packet.h
> > @@ -41,6 +41,7 @@ void set_vsc_packet_colorimetry_data(
> >  		enum dc_color_space cs,
> >  		enum color_transfer_func tf);
> >  
> > +bool is_hdmi_vic_mode(const struct dc_stream_state *stream);
> >  void mod_build_vsc_infopacket(const struct dc_stream_state *stream,
> >  		struct dc_info_packet *info_packet,
> >  		enum dc_color_space cs,
> > diff --git a/drivers/gpu/drm/amd/display/modules/info_packet/info_packet.c b/drivers/gpu/drm/amd/display/modules/info_packet/info_packet.c
> > index 53e488fdb4ea..829cce9455db 100644
> > --- a/drivers/gpu/drm/amd/display/modules/info_packet/info_packet.c
> > +++ b/drivers/gpu/drm/amd/display/modules/info_packet/info_packet.c
> > @@ -23,12 +23,13 @@
> >   *
> >   */
> >  
> > -#include "mod_info_packet.h"
> > +#include "amdgpu.h"
> >  #include "core_types.h"
> > -#include "dc_types.h"
> > -#include "mod_shared.h"
> > -#include "mod_freesync.h"
> >  #include "dc.h"
> > +#include "dc_types.h"
> > +#include "mod_freesync.h"
> > +#include "mod_info_packet.h"
> > +#include "mod_shared.h"
> >  
> >  enum vsc_packet_revision {
> >  	vsc_packet_undefined = 0,
> > @@ -54,6 +55,12 @@ enum vsc_packet_revision {
> >  #define HF_VSIF_3D_BIT   0
> >  #define HF_VSIF_ALLM_BIT 1
> >  
> > +enum allm_trigger_mode {
> > +	ALLM_MODE_DISABLED        = 0,
> > +	ALLM_MODE_ENABLED_DYNAMIC = 1,
> > +	ALLM_MODE_ENABLED_FORCED  = 2,
> > +};
> > +
> >  // VTEM Byte Offset
> >  #define VTEM_PB0		0
> >  #define VTEM_PB1		1
> > @@ -499,7 +506,32 @@ void mod_build_vsc_infopacket(const struct dc_stream_state *stream,
> >  	}
> >  }
> >  
> > -static bool is_hdmi_vic_mode(const struct dc_stream_state *stream)
> > +static bool is_hdmi_allm_mode(const struct dc_stream_state *stream)
> > +{
> > +	/* No local sink */
> > +	if (!stream->link->local_sink)
> > +		return false;
> > +
> > +	/* Sink doesn't expose ALLM support in edid */
> > +	if (!stream->link->local_sink->edid_caps.allm)
> > +		return false;
> > +
> > +	switch (amdgpu_allm_mode) {
> > +	case ALLM_MODE_DISABLED:
> > +		return false;
> > +
> > +	case ALLM_MODE_ENABLED_DYNAMIC:
> > +		break;
> > +
> > +	case ALLM_MODE_ENABLED_FORCED:
> > +		return true;
> > +	}
> > +
> > +	return stream->content_type == DISPLAY_CONTENT_TYPE_GAME ||
> > +	       stream->vrr_active_variable;
> > +}
> > +
> > +bool is_hdmi_vic_mode(const struct dc_stream_state *stream)
> >  {
> >  	if (stream->timing.hdmi_vic == 0)
> >  		return false;
> > @@ -512,7 +544,7 @@ static bool is_hdmi_vic_mode(const struct dc_stream_state *stream)
> >  	if (stream->view_format != VIEW_3D_FORMAT_NONE)
> >  		return false;
> >  
> > -	if (stream->link->local_sink->edid_caps.allm)
> > +	if (is_hdmi_allm_mode(stream))
> >  		return false;
> >  
> >  	return true;
> > @@ -541,7 +573,7 @@ void mod_build_hf_vsif_infopacket(const struct dc_stream_state *stream,
> >  
> >  		info_packet->valid = false;
> >  
> > -		allm = stream->link->local_sink->edid_caps.allm;
> > +		allm = is_hdmi_allm_mode(stream);
> >  		format = stream->view_format == VIEW_3D_FORMAT_NONE ?
> >  			 TIMING_3D_FORMAT_NONE :
> >  			 stream->timing.timing_3d_format;