> Il 17/03/2021 09:19 Tomi Valkeinen <tomba@xxxxxxxxxx> ha scritto:
>
>
> 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...
I prefer lcd_clk_rate.
How about adding an additional patch that changes the variable names to make
the code more readable?
req_rate -> lcd_pclk_rate
clk_rate -> real_lcd_clk_rate
And add a comment to the function which highlights the relationship
LCD_CLK = LCD_PCLK * CLDIV ?
>
> > + 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.
Yes, I agree.
Thanks and regards,
Dario
>
> Tomi
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