Re: [PATCH v2 5/6] drm/panel: st7703: Drive XBD599 panel at higher clock rate

From: "Jernej Škrabec" <jernej.skrabec@gmail.com>
To: "Michael Turquette" <mturquette@baylibre.com>,
	"Stephen Boyd" <sboyd@kernel.org>, "Chen-Yu Tsai" <wens@csie.org>,
	"Samuel Holland" <samuel@sholland.org>,
	"Guido Günther" <agx@sigxcpu.org>,
	"Purism Kernel Team" <kernel@puri.sm>,
	"Ondrej Jirman" <megi@xff.cz>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Jessica Zhang" <quic_jesszhan@quicinc.com>,
	"Sam Ravnborg" <sam@ravnborg.org>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@gmail.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Frank Oltmanns" <frank@oltmanns.dev>
Cc: linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
	Frank Oltmanns <frank@oltmanns.dev>
Subject: Re: [PATCH v2 5/6] drm/panel: st7703: Drive XBD599 panel at higher clock rate
Date: Mon, 05 Feb 2024 18:59:11 +0100	[thread overview]
Message-ID: <13445659.uLZWGnKmhe@jernej-laptop> (raw)
In-Reply-To: <20240205-pinephone-pll-fixes-v2-5-96a46a2d8c9b@oltmanns.dev>

Dne ponedeljek, 05. februar 2024 ob 16:22:28 CET je Frank Oltmanns napisal(a):
> This panel is used in the pinephone that runs on a Allwinner A64 SOC.
> The SOC requires pll-mipi to run at more than 500 MHz.
> 
> This is the relevant clock tree:
>  pll-mipi
>     tcon0
>        tcon-data-clock
> 
> tcon-data-clock has to run at 1/4 the DSI per-lane bit rate. The XBD599
> has 24 bpp and 4 lanes. Therefore, the resulting requested
> tcon-data-clock rate is:
>     crtc_clock * 1000 * (24 / 4) / 4
> 
> tcon-data-clock runs at tcon0 / 4 (fixed divisor), so it requests a
> parent rate of
>     4 * (crtc_clock * 1000 * (24 / 4) / 4)
> 
> Since tcon0 is a ccu_mux, the rate of tcon0 equals the rate of pll-mipi.
> 
> pll-mipi's constraint to run at 500MHz or higher forces us to have a
> crtc_clock >= 83333 kHz if we want a 60 Hz vertical refresh rate.
> 
> Change [hv]sync_(start|end) so that we reach a clock rate of 83502 kHz
> so that it is high enough to align with pll-pipi limits.

Typo: pll-pipi -> pll-mipi

Best regards,
Jernej

> 
> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
> ---
>  drivers/gpu/drm/panel/panel-sitronix-st7703.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7703.c b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> index b55bafd1a8be..6886fd7f765e 100644
> --- a/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> +++ b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
> @@ -320,14 +320,14 @@ static int xbd599_init_sequence(struct st7703 *ctx)
>  
>  static const struct drm_display_mode xbd599_mode = {
>  	.hdisplay    = 720,
> -	.hsync_start = 720 + 40,
> -	.hsync_end   = 720 + 40 + 40,
> -	.htotal	     = 720 + 40 + 40 + 40,
> +	.hsync_start = 720 + 65,
> +	.hsync_end   = 720 + 65 + 65,
> +	.htotal      = 720 + 65 + 65 + 65,
>  	.vdisplay    = 1440,
> -	.vsync_start = 1440 + 18,
> -	.vsync_end   = 1440 + 18 + 10,
> -	.vtotal	     = 1440 + 18 + 10 + 17,
> -	.clock	     = 69000,
> +	.vsync_start = 1440 + 30,
> +	.vsync_end   = 1440 + 30 + 22,
> +	.vtotal	     = 1440 + 30 + 22 + 29,
> +	.clock	     = (720 + 65 + 65 + 65) * (1440 + 30 + 22 + 29) * 60 / 1000,
>  	.flags	     = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
>  	.width_mm    = 68,
>  	.height_mm   = 136,
> 
>