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Date:   Wed, 29 Mar 2023 21:56:39 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Frank Oltmanns <frank@oltmanns.dev>
Cc:     Roman Beranek <romanberanek@icloud.com>,
        Chen-Yu Tsai <wens@csie.org>, David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from
 TCON0_DCLK_REG
Message-ID: <20230329195639.iep4rv5rcigu3gj2@penduick>
References: <20230320161636.24411-1-romanberanek@icloud.com>
 <87wn356ni4.fsf@oltmanns.dev>
 <20230327202045.ceeqqwjug4ktxtsf@penduick>
 <87bkkc3bzc.fsf@oltmanns.dev>
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Hi,

On Tue, Mar 28, 2023 at 09:28:19PM +0200, Frank Oltmanns wrote:
> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> @@ -819,6 +819,34 @@ static void sun6i_dsi_encoder_disable(struct drm_enc=
oder *encoder)
>  	regulator_disable(dsi->regulator);
>  }
>=20
> +static bool sun6i_dsi_encoder_mode_fixup(
> +				   struct drm_encoder *encoder,
> +				   const struct drm_display_mode *mode,
> +				   struct drm_display_mode *adjusted_mode)

So, mode_fixup is kind of deprecated in favour of atomic_check

> +{
> +	if (encoder->encoder_type =3D=3D DRM_MODE_ENCODER_DSI) {
> +		/*
> +		 * For DSI the PLL rate has to respect the bits per pixel and
> +		 * number of lanes.
> +		 *
> +		 * According to the BSP code:
> +		 * PLL rate =3D DOTCLOCK * bpp / lanes
> +		 *
> +		 * Therefore, the clock has to be adjusted in order to set the
> +		 * correct PLL rate when actually setting the clock.
> +		 */
> +		struct sun6i_dsi *dsi =3D encoder_to_sun6i_dsi(encoder);
> +		struct mipi_dsi_device *device =3D dsi->device;
> +		u8 bpp =3D mipi_dsi_pixel_format_to_bpp(device->format);
> +		u8 lanes =3D device->lanes;
> +
> +		adjusted_mode->crtc_clock =3D mode->crtc_clock
> +				 * bpp / (lanes * SUN6I_DSI_TCON_DIV);

And that's visible to the userspace, so it's not where we should store
that value. I guess the best way to do something similar would be to
store it into crtc_state, and then reuse it there. But it starts to make
a lot of rather complicated code compared to your previous patch.

Maxime

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