linux-kernel - [PATCH 1/2] drm/vc4: Reject HDMI modes with too high of clocks.

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Message-Id: <20170920225935.14566-1-eric@anholt.net>
Date:   Wed, 20 Sep 2017 15:59:34 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>,
        Peter Robinson <pbrobinson@...hat.com>
Subject: [PATCH 1/2] drm/vc4: Reject HDMI modes with too high of clocks.

Peter Robinson reported issues on Fedora with 4k monitors not having
their modes filtered down to 1920x1080 on Raspberry Pi.  Hopefully
this resolves that.

Cc: Peter Robinson <pbrobinson@...hat.com>
Signed-off-by: Eric Anholt <eric@...olt.net>
---

Note: This is an untested patch, since I'm away from hardware
currently.

 drivers/gpu/drm/vc4/vc4_hdmi.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index fa37a1c07cf6..65826a4f208e 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -694,7 +694,22 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
 	}
 }
 
+static enum drm_mode_status
+vc5_hdmi_encoder_mode_valid(struct drm_encoder *crtc,
+			    const struct drm_display_mode *mode)
+{
+	/* HSM clock must be 108% of the pixel clock.  Additionally,
+	 * the AXI clock needs to be at least 25% of pixel clock, but
+	 * HSM ends up being the limiting factor.
+	 */
+	if (mode->clock > HSM_CLOCK_FREQ / (1000 * 108 / 100))
+		return MODE_CLOCK_HIGH;
+
+	return MODE_OK;
+}
+
 static const struct drm_encoder_helper_funcs vc4_hdmi_encoder_helper_funcs = {
+	.mode_valid = vc5_hdmi_encoder_mode_valid,
 	.disable = vc4_hdmi_encoder_disable,
 	.enable = vc4_hdmi_encoder_enable,
 };
-- 
2.14.1