[RFC][PATCH] drm: kirin: Restrict modes to known good mode clocks

[John Stultz]

Currently the hikey dsi logic cannot generate accurate byte
clocks values for all pixel clock values. Thus if a mode clock
is selected that cannot match the calculated byte clock, the
device will boot with a blank screen.

This patch uses the new mode_valid callback (many thanks to
Jose Abreu for upstreaming it!) to enforces known good mode
clocks for well known resolutions, which should allow the
display to work from given EDID options, and ensures for a given
resolution & refresh, the right mode clock is selected.

Cc: Daniel Vetter <daniel.vetter at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Sean Paul <seanpaul at chromium.org>
Cc: David Airlie <airlied at linux.ie>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Xinliang Liu <xinliang.liu at linaro.org>
Cc: Xinliang Liu <z.liuxinliang at hisilicon.com>
Cc: Rongrong Zou <zourongrong at gmail.com>
Cc: Xinwei Kong <kong.kongxinwei at hisilicon.com>
Cc: Chen Feng <puck.chen at hisilicon.com>
Cc: Jose Abreu <Jose.Abreu at synopsys.com>
Cc: Archit Taneja <architt at codeaurora.org>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz at linaro.org>
---
 drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c | 37 ++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c b/drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c
index f77dcfa..a84f4bb 100644
--- a/drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c
+++ b/drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c
@@ -603,6 +603,42 @@ static void dsi_encoder_enable(struct drm_encoder *encoder)
 	dsi->enable = true;
 }
 
+static enum drm_mode_status dsi_encoder_mode_valid(struct drm_encoder *crtc,
+					const struct drm_display_mode *mode)
+{
+	/*
+	 * kirin cannot generate all modes, so use the whitelist below
+	 */
+	DRM_DEBUG("%s: Checking mode %ix%i@%i clock: %i...", __func__,
+		mode->hdisplay, mode->vdisplay, drm_mode_vrefresh(mode), mode->clock);
+	if ((mode->hdisplay == 1920 && mode->vdisplay == 1080 && mode->clock == 148500) ||
+	    (mode->hdisplay == 1920 && mode->vdisplay == 1080 && mode->clock == 80192)  ||
+	    (mode->hdisplay == 1920 && mode->vdisplay == 1080 && mode->clock == 74250)  ||
+	    (mode->hdisplay == 1920 && mode->vdisplay == 1080 && mode->clock == 61855)  ||
+	    (mode->hdisplay == 1680 && mode->vdisplay == 1050 && mode->clock == 147116) ||
+	    (mode->hdisplay == 1680 && mode->vdisplay == 1050 && mode->clock == 146250) ||
+	    (mode->hdisplay == 1680 && mode->vdisplay == 1050 && mode->clock == 144589) ||
+	    (mode->hdisplay == 1600 && mode->vdisplay == 1200 && mode->clock == 160961) ||
+	    (mode->hdisplay == 1600 && mode->vdisplay == 900  && mode->clock == 118963) ||
+	    (mode->hdisplay == 1440 && mode->vdisplay == 900  && mode->clock == 126991) ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 1024 && mode->clock == 128946) ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 1024 && mode->clock == 98619)  ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 960  && mode->clock == 102081) ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 800  && mode->clock == 83496)  ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 720  && mode->clock == 74440)  ||
+	    (mode->hdisplay == 1280 && mode->vdisplay == 720  && mode->clock == 74250)  ||
+	    (mode->hdisplay == 1024 && mode->vdisplay == 768  && mode->clock == 78800)  ||
+	    (mode->hdisplay == 1024 && mode->vdisplay == 768  && mode->clock == 75000)  ||
+	    (mode->hdisplay == 1024 && mode->vdisplay == 768  && mode->clock == 81833)  ||
+	    (mode->hdisplay == 800  && mode->vdisplay == 600  && mode->clock == 48907)  ||
+	    (mode->hdisplay == 800  && mode->vdisplay == 600  && mode->clock == 40000)) {
+		DRM_DEBUG("OK\n");
+		return MODE_OK;
+	}
+	DRM_DEBUG("BAD\n");
+	return MODE_BAD;
+}
+
 static void dsi_encoder_mode_set(struct drm_encoder *encoder,
 				 struct drm_display_mode *mode,
 				 struct drm_display_mode *adj_mode)
@@ -622,6 +658,7 @@ static int dsi_encoder_atomic_check(struct drm_encoder *encoder,
 
 static const struct drm_encoder_helper_funcs dw_encoder_helper_funcs = {
 	.atomic_check	= dsi_encoder_atomic_check,
+	.mode_valid	= dsi_encoder_mode_valid,
 	.mode_set	= dsi_encoder_mode_set,
 	.enable		= dsi_encoder_enable,
 	.disable	= dsi_encoder_disable
-- 
2.7.4