linux-kernel - Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK

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Message-ID: <87bkkaonkr.fsf@oltmanns.dev>
Date:   Thu, 30 Mar 2023 06:41:44 +0200
From:   Frank Oltmanns <frank@...manns.dev>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Roman Beranek <romanberanek@...oud.com>,
        Chen-Yu Tsai <wens@...e.org>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from
 TCON0_DCLK_REG


Hi,

On 2023-03-29 at 21:56:39 +0200, Maxime Ripard <maxime@...no.tech> wrote:
> 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_encoder *encoder)
>>  	regulator_disable(dsi->regulator);
>>  }
>>
>> +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

I see. Thanks for pointing that out.

>> +{
>> +	if (encoder->encoder_type == 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 = 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 = encoder_to_sun6i_dsi(encoder);
>> +		struct mipi_dsi_device *device = dsi->device;
>> +		u8 bpp = mipi_dsi_pixel_format_to_bpp(device->format);
>> +		u8 lanes = device->lanes;
>> +
>> +		adjusted_mode->crtc_clock = 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.

Ah, interesting. But I agree, let's stick to the simpler aproach.

Thanks,
  Frank

>
> Maxime
>
> [[End of PGP Signed Part]]

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