On Mon, Aug 11, 2025 at 09:46:55AM +0300, Lee, Shawn C wrote:
> On Fri, Aug 08, 2025 at 09:40:00AM +0000, Imre Deak C wrote:
> >On Fri, Aug 08, 2025 at 09:16:02AM +0000, Lee Shawn C wrote:
> >> While performing HDMI compliance testing, test equipment may request
> >> different bpc output for signal measurement. However, display driver
> >> typically determines the maximum available bpc based on HW bandwidth.
> >>
> >> Introduce a new debugfs that allows user to configure dedicated bpc
> >> manually, and making HDMI compliance test much easier.
> >>
> >> v2: Using exist variable max_requested_bpc.
> >
> > How come this doesn't get reset after a hotplug as you described for
> > the case when the property is used, even though both the property and
> > this debug entries use the same state variable? (Not saying that the
> > reset happing after a hotplug is a valid justification for a new
> > debugfs entry, the hotplug could be also handled by the user, but you
> > could argue the debugfs entry is more convenient.)
>
> Hi Imre, thank you for the prompt response.
>
> https://elixir.bootlin.com/linux/v6.16/source/drivers/gpu/drm/i915/display/intel_hdmi.c#L2672
>
> The max_bpc_property and max_bpc values are initialized during
> connector initialization process.
>
> https://elixir.bootlin.com/linux/v6.16/source/drivers/gpu/drm/drm_atomic.c#L468
>
> The max_bpc will be restored to info->bpc (from EDID) at
> drm_atomic_connector_check() everytime.
>
> When max_bpc_property is available, this funciton also compares
> max_bpc with max_requested_bpc and updates max_bpc to the smaller of
> the two values.
>
> The i915 display driver then relies on this max_bpc value to determine
> whether to update the pipe bpp value in compute_sink_pipe_bpp().
> Therefore, we can simply update max_requested_bpc to affect pipe bpp
> output. And no additional driver changes are required.
The point above was to figure out how the "max bpc" connector property
gets reset after a hotplug, based on your earlier explanation for the
reason to add a debugfs entry instead. But based on the above and also
based on my tests, that connector property actually keeps its value
across hotplugs.
So I think that the property could be used for your tests then, or if
you wanted to have a debugfs entry for convenience, then the
intel_force_link_bpp debugfs entry could be added for all HDMI
connectors, as suggested earlier, instead of adding a new debugfs entry.
The following would do that, could you give it a go?
diff --git a/drivers/gpu/drm/i915/display/g4x_hdmi.c
b/drivers/gpu/drm/i915/display/g4x_hdmi.c
index 108ebd97f9e4..b31fb1e4bc1a 100644
--- a/drivers/gpu/drm/i915/display/g4x_hdmi.c
+++ b/drivers/gpu/drm/i915/display/g4x_hdmi.c
@@ -136,11 +136,8 @@ static int g4x_hdmi_compute_config(struct intel_encoder
*encoder,
struct intel_atomic_state *state =
to_intel_atomic_state(crtc_state->uapi.state);
struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
- if (HAS_PCH_SPLIT(display)) {
+ if (HAS_PCH_SPLIT(display))
crtc_state->has_pch_encoder = true;
- if (!intel_fdi_compute_pipe_bpp(crtc_state))
- return -EINVAL;
- }
if (display->platform.g4x)
crtc_state->has_hdmi_sink = g4x_compute_has_hdmi_sink(state,
crtc);
diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c
b/drivers/gpu/drm/i915/display/intel_hdmi.c
index cbee628eb26b..027e8ed0cea8 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -55,6 +55,7 @@
#include "intel_display_regs.h"
#include "intel_display_types.h"
#include "intel_dp.h"
+#include "intel_fdi.h"
#include "intel_gmbus.h"
#include "intel_hdcp.h"
#include "intel_hdcp_regs.h"
@@ -2345,6 +2346,9 @@ int intel_hdmi_compute_config(struct intel_encoder
*encoder,
if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
pipe_config->pixel_multiplier = 2;
+ if (!intel_fdi_compute_pipe_bpp(pipe_config))
+ return -EINVAL;
+
pipe_config->has_audio =
intel_hdmi_has_audio(encoder, pipe_config, conn_state) &&
intel_audio_compute_config(encoder, pipe_config, conn_state);
diff --git a/drivers/gpu/drm/i915/display/intel_link_bw.c
b/drivers/gpu/drm/i915/display/intel_link_bw.c
index 3caef7f9c7c4..9e8220d86a4a 100644
--- a/drivers/gpu/drm/i915/display/intel_link_bw.c
+++ b/drivers/gpu/drm/i915/display/intel_link_bw.c
@@ -449,6 +449,7 @@ void intel_link_bw_connector_debugfs_add(struct
intel_connector *connector)
switch (connector->base.connector_type) {
case DRM_MODE_CONNECTOR_DisplayPort:
case DRM_MODE_CONNECTOR_eDP:
+ case DRM_MODE_CONNECTOR_HDMIA:
break;
case DRM_MODE_CONNECTOR_VGA:
case DRM_MODE_CONNECTOR_SVIDEO:
@@ -456,13 +457,6 @@ void intel_link_bw_connector_debugfs_add(struct
intel_connector *connector)
case DRM_MODE_CONNECTOR_DVID:
if (HAS_FDI(display))
break;
-
- return;
- case DRM_MODE_CONNECTOR_HDMIA:
- if (HAS_FDI(display) && !HAS_DDI(display))
- break;
-
- return;
default:
return;
}
