Re: [PATCH v3 2/6] drm/bridge: tc358767: Use tc_pxl_pll_calc() to correct adjusted_mode clock

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Am Sonntag, 23. Juni 2024, 16:38:34 CEST schrieb Marek Vasut:
> Use tc_pxl_pll_calc() to find out the exact clock frequency generated by the
> Pixel PLL. Use the Pixel PLL frequency as adjusted_mode clock frequency and
> pass it down the display pipeline to obtain exactly this frequency on input
> into this bridge.
> 
> The precise input frequency that matches the Pixel PLL frequency is
> important for this bridge, as if the frequencies do not match, the
> bridge does suffer VFIFO overruns or underruns.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>

This changes actually changes the media_disp1_pix clock to match the
configured PLL rate in the bridge. 147333000 instead of 148500000.

Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
> Cc: Jonas Karlman <jonas@kwiboo.se>
> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Neil Armstrong <neil.armstrong@linaro.org>
> Cc: Robert Foss <rfoss@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: dri-devel@lists.freedesktop.org
> Cc: kernel@dh-electronics.com
> ---
> V2: - Use mode clock as input into tc_pxl_pll_calc() to avoid
>       accumulating rounding error
> V3: No change
> ---
>  drivers/gpu/drm/bridge/tc358767.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index cbb342d811ac3..20be21660ba76 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -1619,6 +1619,18 @@ static int tc_dpi_atomic_check(struct drm_bridge *bridge,
>  			       struct drm_crtc_state *crtc_state,
>  			       struct drm_connector_state *conn_state)
>  {
> +	struct tc_data *tc = bridge_to_tc(bridge);
> +	int adjusted_clock = 0;
> +	int ret;
> +
> +	ret = tc_pxl_pll_calc(tc, clk_get_rate(tc->refclk),
> +			      crtc_state->mode.clock * 1000,
> +			      &adjusted_clock, NULL);
> +	if (ret)
> +		return ret;
> +
> +	crtc_state->adjusted_mode.clock = adjusted_clock / 1000;
> +
>  	/* DSI->DPI interface clock limitation: upto 100 MHz */
>  	if (crtc_state->adjusted_mode.clock > 100000)
>  		return -EINVAL;
> @@ -1631,6 +1643,18 @@ static int tc_edp_atomic_check(struct drm_bridge *bridge,
>  			       struct drm_crtc_state *crtc_state,
>  			       struct drm_connector_state *conn_state)
>  {
> +	struct tc_data *tc = bridge_to_tc(bridge);
> +	int adjusted_clock = 0;
> +	int ret;
> +
> +	ret = tc_pxl_pll_calc(tc, clk_get_rate(tc->refclk),
> +			      crtc_state->mode.clock * 1000,
> +			      &adjusted_clock, NULL);
> +	if (ret)
> +		return ret;
> +
> +	crtc_state->adjusted_mode.clock = adjusted_clock / 1000;
> +
>  	/* DPI->(e)DP interface clock limitation: upto 154 MHz */
>  	if (crtc_state->adjusted_mode.clock > 154000)
>  		return -EINVAL;
> 


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