On 09/29/16 19:43, Bartosz Golaszewski wrote:
> Some architectures don't use the common clock framework and don't
> implement all the clk interfaces for every clock. This is the case
> for da850-lcdk where clk_set_rate() only works for PLL0 and PLL1.
>
> Trying to set the clock rate for the LCDC clock results in -EINVAL
> being returned.
>
> As a workaround for that: if the call to clk_set_rate() fails, fall
> back to adjusting the clock divider instead. Proper divider value is
> calculated by dividing the current clock rate by the required pixel
> clock rate in HZ.
>
> This code is based on a hack initially developed internally for
> baylibre by Karl Beldan <kbeldan@xxxxxxxxxxxx>.
>
> Tested with a da850-lcdk with an LCD display connected over VGA.
>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
Forgot to mention, but I've picked this up too, but I won't send a pull
request for 4.9 anymore.
BR,
Jyri
> ---
> v1 -> v2:
> - rebased on top of current drm-next
> - removed unnecessary error messages
> - removed an extra newline
> - added a warning if the effective pixel clock rate differs much from
> the requested rate
>
> v2 -> v3:
> - removed WARN_ONCE() in favor of dev_warn()
> - added the real and calculated clock rates to the warning message
> - tweaked the variable names
> - used a local variable to remove redundant 'crtc->mode.clock * 1000'
>
> Retested with
>
> modetest -M tilcdc -s 26:800x600@RG16
> modetest -M tilcdc -s 26:1024x768@RG16
>
> using some additional work-in-progress changes on top of this patch.
>
> drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 57 ++++++++++++++++++++++++++++++++----
> 1 file changed, 51 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> index 52ebe8f..87cfde9 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> @@ -320,23 +320,68 @@ static bool tilcdc_crtc_mode_fixup(struct drm_crtc *crtc,
> return true;
> }
>
> +/*
> + * Calculate the percentage difference between the requested pixel clock rate
> + * and the effective rate resulting from calculating the clock divider value.
> + */
> +static unsigned int tilcdc_pclk_diff(unsigned long rate,
> + unsigned long real_rate)
> +{
> + int r = rate / 100, rr = real_rate / 100;
> +
> + return (unsigned int)(abs(((rr - r) * 100) / r));
> +}
> +
> 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);
> - const unsigned clkdiv = 2; /* using a fixed divider of 2 */
> + unsigned long clk_rate, real_rate, req_rate;
> + unsigned int clkdiv;
> int ret;
>
> + clkdiv = 2; /* first try using a standard divider of 2 */
> +
> /* mode.clock is in KHz, set_rate wants parameter in Hz */
> - ret = clk_set_rate(priv->clk, crtc->mode.clock * 1000 * clkdiv);
> + req_rate = crtc->mode.clock * 1000;
> +
> + ret = clk_set_rate(priv->clk, req_rate * clkdiv);
> + clk_rate = clk_get_rate(priv->clk);
> if (ret < 0) {
> - dev_err(dev->dev, "failed to set display clock rate to: %d\n",
> - crtc->mode.clock);
> - return;
> + /*
> + * If we fail to set the clock rate (some architectures don't
> + * use the common clock framework yet and may not implement
> + * all the clk API calls for every clock), try the next best
> + * thing: adjusting the clock divider, unless clk_get_rate()
> + * failed as well.
> + */
> + if (!clk_rate) {
> + /* Nothing more we can do. Just bail out. */
> + dev_err(dev->dev,
> + "failed to set the pixel clock - unable to read current lcdc clock rate\n");
> + return;
> + }
> +
> + clkdiv = DIV_ROUND_CLOSEST(clk_rate, req_rate);
> +
> + /*
> + * Emit a warning if the real clock rate resulting from the
> + * calculated divider differs much from the requested rate.
> + *
> + * 5% is an arbitrary value - LCDs are usually quite tolerant
> + * about pixel clock rates.
> + */
> + real_rate = clkdiv * req_rate;
> +
> + if (tilcdc_pclk_diff(clk_rate, real_rate) > 5) {
> + dev_warn(dev->dev,
> + "effective pixel clock rate (%luHz) differs from the calculated rate (%luHz)\n",
> + clk_rate, real_rate);
> + }
> }
>
> - tilcdc_crtc->lcd_fck_rate = clk_get_rate(priv->clk);
> + tilcdc_crtc->lcd_fck_rate = clk_rate;
>
> DBG("lcd_clk=%u, mode clock=%d, div=%u",
> tilcdc_crtc->lcd_fck_rate, crtc->mode.clock, clkdiv);
>
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