On 14/03/2021 17:13, Dario Binacchi wrote:
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
The above doesn't make sense, the code already sets LCD_CLK to 'req_rate
* clkdiv', not req_rate.
and the real LCD_CLK rate must be compared with 'req_rate * CLKDIV' and
not with req_rate.
This is true, the code looks at the wrong value.
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@xxxxxxxxx>
---
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;
"clk_div_rate" sounds a bit odd to me. Why not lcd_fck_rate, as that's
the name used later? Or lcd_clk_rate. Or maybe lcd_clk_req_rate...
+ 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
I think this fix is fine, but looking at the current code, it's calling
tilcdc_pclk_diff(), but doesn't actually provide pixel clocks to the
function, but fclk.
Tomi
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