linux-kernel - [PATCH 7/8] drm/tidss: Fix clock request value for OLDI videoports

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Date:   Tue, 19 Jul 2022 13:38:44 +0530
From:   Aradhya Bhatia <a-bhatia1@...com>
To:     Tomi Valkeinen <tomba@...nel.org>, Jyri Sarha <jyri.sarha@....fi>,
        Rob Herring <robh+dt@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
CC:     Darren Etheridge <detheridge@...com>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rahul T R <r-ravikumar@...com>,
        Krunal Bhargav <k-bhargav@...com>,
        Devarsh Thakkar <devarsht@...com>,
        DRI Development List <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: [PATCH 7/8] drm/tidss: Fix clock request value for OLDI videoports

The OLDI TX(es) require a serial clock which is 7 times the pixel clock
of the display panel. When the OLDI is enabled in DSS, the pixel clock
input of the corresponding videoport gets a divided-by 7 value of the
requested clock.

For the am625-dss, the requested clock needs to be 7 times the value.

Update the clock frequency by requesting 7 times the value.

Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
---
 drivers/gpu/drm/tidss/tidss_dispc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index c4a5f808648f..0b9689453ee8 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -1326,6 +1326,16 @@ int dispc_vp_set_clk_rate(struct dispc_device *dispc, u32 hw_videoport,
 	int r;
 	unsigned long new_rate;
 
+	/*
+	 * For AM625 OLDI video ports, the requested pixel clock needs to take into account the
+	 * serial clock required for the serialization of DPI signals into LVDS signals. The
+	 * incoming pixel clock on the OLDI video port gets divided by 7 whenever OLDI enable bit
+	 * gets set.
+	 */
+	if (dispc->feat->vp_bus_type[hw_videoport] == DISPC_VP_OLDI &&
+	    dispc->feat->subrev == DISPC_AM625)
+		rate *= 7;
+
 	r = clk_set_rate(dispc->vp_clk[hw_videoport], rate);
 	if (r) {
 		dev_err(dispc->dev, "vp%d: failed to set clk rate to %lu\n",
-- 
2.37.0