Messages in this thread | | | Subject | Re: [PATCH] drm/tilcdc: fix LCD pixel clock setting | From | Tomi Valkeinen <> | Date | Wed, 17 Mar 2021 10:19:46 +0200 |
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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@libero.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;
"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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