On 12/14/2022 9:16 AM, Murthy, Arun R wrote:
-----Original Message-----
From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of Ankit
Nautiyal
Sent: Tuesday, December 13, 2022 11:21 AM
To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Subject: [PATCH] drm/i915/hdmi: Go for scrambling only if
platform supports TMDS clock > 340MHz
There are cases, where devices have an HDMI1.4 retimer, and TMDS clock
rate is capped to 340MHz via VBT. In such cases scrambling might be
supported by the platform and an HDMI2.0 sink for lower TMDS rates, but
not supported by the retimer, causing blankouts.
So avoid enabling scrambling, if the TMDS clock is capped to <= 340MHz.
Doesn't this clash with scrambling with low rates?
Hi Arun,
As per HDMI 2.0 spec, scrambling is always required when TMDS char rate
> 340Mcsc
So scrambling is optional for rate <= 340, if source and sink both
support scrambling, it is enabled by the source.
Gen 10 onward HDMI 2.0 is supported, the max tmds clock is 594MHz, and
scrambling is supported.
But there seem to be cases where for certain platforms that support HDMI
2.0, there is an HDMI1.4 retimer chip and the max tmds clock is capped
by VBT to less than 340MHz.
In such cases when an HDMI2.0 sink is connected, the driver checks for
Gen >= 10 + sink scrambling support, and goes with scrambling even for
resolutions that require lower clocks.
This creates problem as HDMI1.4 retimer chip doesn't support scrambling.
So in this patch, we replace the check for Gen >=10 with check if max
source TMDS clock > 340 MHz (taking into account the VBT capping).
In general case for Gen>= 10 (when VBT does not restrict the max tmds
clock), if sink also supports scrambling for lower rate, driver will go
with scrambling with lower clocks too.
Thanks & Regards,
Ankit
Thanks and Regards,
Arun R Murthy
--------------------
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
---
drivers/gpu/drm/i915/display/intel_hdmi.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c
b/drivers/gpu/drm/i915/display/intel_hdmi.c
index efa2da080f62..c124fe667bc0 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -2244,6 +2244,11 @@ static bool intel_hdmi_is_cloned(const struct
intel_crtc_state *crtc_state)
!is_power_of_2(crtc_state->uapi.encoder_mask);
}
+static bool source_can_support_scrambling(struct intel_encoder
+*encoder) {
+ return intel_hdmi_source_max_tmds_clock(encoder) > 340000; }
+
int intel_hdmi_compute_config(struct intel_encoder *encoder,
struct intel_crtc_state *pipe_config,
struct drm_connector_state *conn_state) @@ -
2301,7 +2306,7 @@ int intel_hdmi_compute_config(struct intel_encoder
*encoder,
pipe_config->lane_count = 4;
- if (scdc->scrambling.supported && DISPLAY_VER(dev_priv) >= 10) {
+ if (scdc->scrambling.supported &&
+source_can_support_scrambling(encoder)) {
if (scdc->scrambling.low_rates)
pipe_config->hdmi_scrambling = true;
--
2.25.1
