linux-kernel - [PATCH] drm/tilcdc: fix LCD pixel clock setting

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Date:   Sun, 14 Mar 2021 16:13:41 +0100
From:   Dario Binacchi <dariobin@...ero.it>
To:     linux-kernel@...r.kernel.org
Cc:     Dario Binacchi <dariobin@...ero.it>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jyri Sarha <jyri.sarha@....fi>,
        Tomi Valkeinen <tomba@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH] drm/tilcdc: fix LCD pixel clock setting

As reported by TI spruh73x RM, the LCD pixel clock (LCD_PCLK) frequency
is obtained by dividing LCD_CLK, the LCD controller reference clock,
for CLKDIV:

LCD_PCLK = LCD_CLK / CLKDIV

where CLKDIV must be greater than 1.

Therefore LCD_CLK must be set to 'req_rate * CLKDIV' instead of req_rate
and the real LCD_CLK rate must be compared with 'req_rate * CLKDIV' and
not with req_rate.
Passing req_rate instead of 'req_rate * CLKDIV' to the tilcdc_pclk_diff
routine caused it to fail even if LCD_CLK was properly set.

Signed-off-by: Dario Binacchi <dariobin@...ero.it>

---

 drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
index 30213708fc99..02f56c9a5da5 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
@@ -203,7 +203,7 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct tilcdc_drm_private *priv = dev->dev_private;
 	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
-	unsigned long clk_rate, real_rate, req_rate;
+	unsigned long clk_rate, real_rate, req_rate, clk_div_rate;
 	unsigned int clkdiv;
 	int ret;
 
@@ -211,10 +211,11 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
 
 	/* mode.clock is in KHz, set_rate wants parameter in Hz */
 	req_rate = crtc->mode.clock * 1000;
-
-	ret = clk_set_rate(priv->clk, req_rate * clkdiv);
+	/* LCD clock divisor input rate */
+	clk_div_rate = req_rate * clkdiv;
+	ret = clk_set_rate(priv->clk, clk_div_rate);
 	clk_rate = clk_get_rate(priv->clk);
-	if (ret < 0 || tilcdc_pclk_diff(req_rate, clk_rate) > 5) {
+	if (ret < 0 || tilcdc_pclk_diff(clk_div_rate, clk_rate) > 5) {
 		/*
 		 * If we fail to set the clock rate (some architectures don't
 		 * use the common clock framework yet and may not implement
-- 
2.17.1