On Tue, 25 Oct 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx> wrote:
> According to BSpec, cdclk has to be not less than 432 MHz with DP audio
> enabled, port width x4, and link rate HBR2 (5.4 GHz)
>
> Having a lower cdclk triggers pipe underruns, which then lead to displays
> continuously cycling off and on. This is essential for DP MST audio as the
> link is trained at HBR2 and 4 lanes by default.
>
> v2: Restrict fix to BDW
> Retain the set cdclk across modesets (Ville)
Cc: stable@xxxxxxxxxxxxxxx
>
> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_display.c | 28 +++++++++++++++++++++++++---
> 1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index a94f7d1..8c59651 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10260,6 +10260,18 @@ static void bxt_modeset_commit_cdclk(struct drm_atomic_state *old_state)
> bxt_set_cdclk(to_i915(dev), req_cdclk);
> }
>
> +static unsigned int bdw_dp_audio_cdclk(struct intel_crtc_state *crtc_state)
> +{
> +
> + if (intel_crtc_has_dp_encoder(crtc_state) &&
> + crtc_state->has_audio &&
> + crtc_state->port_clock >= 540000 &&
> + crtc_state->lane_count == 4)
> + return 432000;
Where does 432000 come from? 450000 or even (337500 + 1). See below.
> +
> + return 0;
> +}
> +
> /* compute the max rate for new configuration */
> static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> {
> @@ -10275,7 +10287,7 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> sizeof(intel_state->min_pixclk));
>
> for_each_crtc_in_state(state, crtc, cstate, i) {
> - int pixel_rate;
> + unsigned int pixel_rate;
>
> crtc_state = to_intel_crtc_state(cstate);
> if (!crtc_state->base.enable) {
> @@ -10285,9 +10297,19 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
>
> pixel_rate = ilk_pipe_pixel_rate(crtc_state);
>
> + if (IS_BROADWELL(dev_priv)) {
> /* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
> - if (IS_BROADWELL(dev_priv) && crtc_state->ips_enabled)
> - pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
> + if (crtc_state->ips_enabled)
> + pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
> +
> + /* BSpec says "Do not use DisplayPort with CDCLK less than
> + * 432 MHz, audio enabled, port width x4, and link rate
For me the spec says "Do not use DisplayPort with CDCLK 337.5 MHz", not
"less than 432 MHz".
> + * HBR2 (5.4 GHz), or else there may be audio corruption or
> + * screen corruption."
> + */
> + pixel_rate = max(pixel_rate,
> + bdw_dp_audio_cdclk(crtc_state));
> + }
I'd add a new function
static int bwd_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
int pixel_rate)
and do both the IPS adjustment and the audio adjustment there, returning
the original pixel_rate if adjustment is not needed. Move the comments
there as well.
It would be called as
if (IS_BROADWELL(dev_priv))
pixel_rate = bwd_adjust_min_pipe_pixel_rate(crtc_state, pixel_rate);
here.
BR,
Jani.
>
> intel_state->min_pixclk[i] = pixel_rate;
> }
--
Jani Nikula, Intel Open Source Technology Center
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