When I connected my cubieboard running 4.15-rc1 to my 4k display I got no picture. Some
digging found that there is no check against the upper pixelclock limit of the HDMI
output, so X selects a 4kp60 format at 594 MHz, which obviously won't work.
The patch below adds a check for the upper bound of what this hardware can do, and
it checks if the requested tmds clock can be obtained.
It also allows for the ± 0.5% pixel clock variation that the HDMI spec permits.
That code is based on commit 22d0be2a557e53a22feb484e8fce255fe09e6ad5 from
Jose Abreu for drm/arc.
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Changes since v3:
- Move the mode_valid callback to struct drm_encoder_helper_funcs.
I'm assuming this is the correct struct, since this check is specific to the
hdmi encoder.
Changes since v2:
- Allow for the 0.5% variation.
---
drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
index dda904ec0534..500b6fb3e028 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
@@ -175,11 +175,31 @@ static void sun4i_hdmi_mode_set(struct drm_encoder *encoder,
writel(val, hdmi->base + SUN4I_HDMI_VID_TIMING_POL_REG);
}
+static enum drm_mode_status sun4i_hdmi_mode_valid(struct drm_encoder *encoder,
+ const struct drm_display_mode *mode)
+{
+ struct sun4i_hdmi *hdmi = drm_encoder_to_sun4i_hdmi(encoder);
+ unsigned long rate = mode->clock * 1000;
+ unsigned long diff = rate / 200; /* +-0.5% allowed by HDMI spec */
+ long rounded_rate;
+
+ /* 165 MHz is the typical max pixelclock frequency for HDMI <= 1.2 */
+ if (rate > 165000000)
+ return MODE_CLOCK_HIGH;
+ rounded_rate = clk_round_rate(hdmi->tmds_clk, rate);
+ if (rounded_rate > 0 &&
+ max_t(unsigned long, rounded_rate, rate) -
+ min_t(unsigned long, rounded_rate, rate) < diff)
+ return MODE_OK;
+ return MODE_NOCLOCK;
+}
+
static const struct drm_encoder_helper_funcs sun4i_hdmi_helper_funcs = {
.atomic_check = sun4i_hdmi_atomic_check,
.disable = sun4i_hdmi_disable,
.enable = sun4i_hdmi_enable,
.mode_set = sun4i_hdmi_mode_set,
+ .mode_valid = sun4i_hdmi_mode_valid,
};
static const struct drm_encoder_funcs sun4i_hdmi_funcs = {
--
2.15.0
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