linux-kernel - [PATCH v3 06/10] drm/bridge: cdns-dsi: Reset the DCS write FIFO

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Date: Mon, 17 Jun 2024 16:23:07 +0530
From: Aradhya Bhatia <a-bhatia1@...com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Tomi Valkeinen
	<tomi.valkeinen@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman
	<jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard
	<mripard@...nel.org>, Jyri Sarha <jyri.sarha@....fi>,
        Thomas Zimmermann
	<tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Daniel Vetter
	<daniel@...ll.ch>
CC: DRI Development List <dri-devel@...ts.freedesktop.org>,
        Linux Kernel List
	<linux-kernel@...r.kernel.org>,
        Dominik Haller <d.haller@...tec.de>, Sam
 Ravnborg <sam@...nborg.org>,
        Thierry Reding <treding@...dia.com>,
        Kieran
 Bingham <kieran.bingham+renesas@...asonboard.com>,
        Nishanth Menon
	<nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Praneeth Bajjuri
	<praneeth@...com>, Udit Kumar <u-kumar1@...com>,
        Devarsh Thakkar
	<devarsht@...com>,
        Jayesh Choudhary <j-choudhary@...com>, Jai Luthra
	<j-luthra@...com>,
        Aradhya Bhatia <a-bhatia1@...com>
Subject: [PATCH v3 06/10] drm/bridge: cdns-dsi: Reset the DCS write FIFO

Allow the DCS Write FIFO in the cdns-dsi controller to reset before any
DCS packet is transmitted to the DSI sink device.

The DCS FIFO reset is optional. Not all panels require it. But at
least one of the DSI based panel that uses Ilitek ILI9881C (DSI to DPI
bridge) doesn't work with without this reset.

Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 05d2f4cc50da..87fdd07ca0bc 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -1037,6 +1037,9 @@ static ssize_t cdns_dsi_transfer(struct mipi_dsi_host *host,
 
 	cdns_dsi_init_link(dsi);
 
+	/* Reset the DCS Write FIFO */
+	writel(0x00, dsi->regs + DIRECT_CMD_FIFO_RST);
+
 	ret = mipi_dsi_create_packet(&packet, msg);
 	if (ret)
 		goto out;
-- 
2.34.1