Currently in intel_dp_mode_valid(), we compute the number of joined
pipes
required before deciding whether DSC is needed. This ordering
prevents us
from accounting for DSC-related overhead when determining pipe
requirements.
It is not possible to first decide whether DSC is needed and then
compute
the required number of joined pipes, because the two depend on each
other:
- DSC need is a function of the pipe count (e.g., 4‑pipe always
requires
DSC; 2‑pipe may require it if uncompressed joiner is unavailable).
- Whether a given pipe‑join configuration is sufficient depends on
effective bandwidth, which itself changes when DSC is used.
As a result, the only correct approach is to iterate candidate pipe
counts.
So, refactor the logic to start with a single pipe and incrementally
try
additional pipes only if needed. While DSC overhead is not yet computed
here, this restructuring prepares the code to support that in a
follow-up
changes.
Additionally, if a forced joiner configuration is present, we first
check
whether it satisfies the bandwidth and timing constraints. If it
does not,
we fall back to evaluating configurations with 1, 2, or 4 pipes joined
and prune or keep the mode accordingly.
v2:
- Iterate over number of pipes to be joined instead of joiner
candidates. (Jani)
- Document the rationale of iterating over number of joined pipes.
(Imre)
Signed-off-by: Ankit Nautiyal <[email protected]>
---
drivers/gpu/drm/i915/display/intel_dp.c | 158
+++++++++++++++---------
1 file changed, 103 insertions(+), 55 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
b/drivers/gpu/drm/i915/display/intel_dp.c
index 4c3a1b6d0015..599965a6e1a6 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1434,6 +1434,23 @@ bool intel_dp_has_dsc(const struct
intel_connector *connector)
return true;
}
+static
+bool intel_dp_can_join(struct intel_display *display,
+ int num_joined_pipes)
+{
+ switch (num_joined_pipes) {
+ case 1:
+ return true;
+ case 2:
+ return HAS_BIGJOINER(display) ||
+ HAS_UNCOMPRESSED_JOINER(display);
+ case 4:
+ return HAS_ULTRAJOINER(display);
+ default:
+ return false;
+ }
+}
+
static enum drm_mode_status
intel_dp_mode_valid(struct drm_connector *_connector,
const struct drm_display_mode *mode)
@@ -1445,13 +1462,13 @@ intel_dp_mode_valid(struct drm_connector
*_connector,
const struct drm_display_mode *fixed_mode;
int target_clock = mode->clock;
int max_rate, mode_rate, max_lanes, max_link_clock;
- int max_dotclk = display->cdclk.max_dotclk_freq;
u16 dsc_max_compressed_bpp = 0;
u8 dsc_slice_count = 0;
enum drm_mode_status status;
bool dsc = false;
int num_joined_pipes;
int link_bpp_x16;
+ int num_pipes;
status = intel_cpu_transcoder_mode_valid(display, mode);
if (status != MODE_OK)
@@ -1488,67 +1505,98 @@ intel_dp_mode_valid(struct drm_connector
*_connector,
target_clock, mode->hdisplay,
link_bpp_x16, 0);
- num_joined_pipes = intel_dp_num_joined_pipes(intel_dp,
connector,
- mode->hdisplay, target_clock);
- max_dotclk *= num_joined_pipes;
-
- if (target_clock > max_dotclk)
- return MODE_CLOCK_HIGH;
-
- status = intel_pfit_mode_valid(display, mode, output_format,
num_joined_pipes);
- if (status != MODE_OK)
- return status;
-
- if (intel_dp_has_dsc(connector)) {
- int pipe_bpp;
-
- /*
- * TBD pass the connector BPC,
- * for now U8_MAX so that max BPC on that platform would be
picked
- */
- pipe_bpp = intel_dp_dsc_compute_max_bpp(connector, U8_MAX);
-
- /*
- * Output bpp is stored in 6.4 format so right shift by 4
to get the
- * integer value since we support only integer values of bpp.
- */
- if (intel_dp_is_edp(intel_dp)) {
- dsc_max_compressed_bpp =
- drm_edp_dsc_sink_output_bpp(connector->dp.dsc_dpcd) >> 4;
-
- dsc_slice_count =
- intel_dp_dsc_get_slice_count(connector,
- target_clock,
- mode->hdisplay,
- num_joined_pipes);
-
- dsc = dsc_max_compressed_bpp && dsc_slice_count;
- } else if
(drm_dp_sink_supports_fec(connector->dp.fec_capability)) {
- unsigned long bw_overhead_flags = 0;
-
- if (!drm_dp_is_uhbr_rate(max_link_clock))
- bw_overhead_flags |= DRM_DP_BW_OVERHEAD_FEC;
-
- dsc = intel_dp_mode_valid_with_dsc(connector,
- max_link_clock, max_lanes,
- target_clock, mode->hdisplay,
- num_joined_pipes,
- output_format, pipe_bpp,
- bw_overhead_flags);
+ /*
+ * We cannot determine the required pipe‑join count before
knowing whether
+ * DSC is needed, nor can we determine DSC need without knowing
the pipe
+ * count.
+ * Because of this dependency cycle, the only correct approach
is to iterate
+ * over candidate pipe counts and evaluate each combination.
+ */
+ for (num_pipes = 0; num_pipes < I915_MAX_PIPES; num_pipes++) {
+ int max_dotclk = display->cdclk.max_dotclk_freq;
+
+ status = MODE_CLOCK_HIGH;
+
+ if (num_pipes == 0) {
+ if (!connector->force_joined_pipes)
+ continue;
+ num_joined_pipes = connector->force_joined_pipes;
+ } else {
+ num_joined_pipes = num_pipes;
+ }
