Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK_REG

[Frank Oltmanns <frank@oltmanns.dev>]

Hi,

On 2023-03-27 at 22:20:45 +0200, Maxime Ripard <maxime@cerno.tech> wrote:
> Hi,
>
> On Sat, Mar 25, 2023 at 12:40:04PM +0100, Frank Oltmanns wrote:
[...]
>> Actually, I had the following third patch prepared that adjusted the dotclock rate so that the
>> required PLL rate is set. But again, this seems very indirect, so that’s why I refrained from
>> submitting it and I submitted the linked patch above instead.
>>
>> Anyway, here is the third proposal:
>>
>> — 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)
>> +{
>> ⁃ 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);
>> ⁃ }
>> ⁃
>>
>> ⁃ return true;
>> +}
>> ⁃ static int sun6i_dsi_get_modes(struct drm_connector *connector)
>>   {
>>       struct sun6i_dsi *dsi = connector_to_sun6i_dsi(connector);
>> @@ -851,6 +879,7 @@ static const struct drm_connector_funcs sun6i_dsi_connector_funcs = {
>>  static const struct drm_encoder_helper_funcs sun6i_dsi_enc_helper_funcs = {
>>  	.disable	= sun6i_dsi_encoder_disable,
>>  	.enable		= sun6i_dsi_encoder_enable,
>> ⁃ .mode_fixup = sun6i_dsi_encoder_mode_fixup,
>>   };
>
> It's not clear to me what this patch is supposed to be doing, there's no mode_fixup implementation
> upstream?
>

Sorry, my mail client tried some fancy formatting. :(

This is the patch again.

--- 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)
+{
+	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);
+	}
+
+	return true;
+}
+
 static int sun6i_dsi_get_modes(struct drm_connector *connector)
 {
 	struct sun6i_dsi *dsi = connector_to_sun6i_dsi(connector);
@@ -851,6 +879,7 @@ static const struct drm_connector_funcs sun6i_dsi_connector_funcs = {
 static const struct drm_encoder_helper_funcs sun6i_dsi_enc_helper_funcs = {
 	.disable	= sun6i_dsi_encoder_disable,
 	.enable		= sun6i_dsi_encoder_enable,
+	.mode_fixup	= sun6i_dsi_encoder_mode_fixup,
 };

 static u32 sun6i_dsi_dcs_build_pkt_hdr(struct sun6i_dsi *dsi,


I still like the original patch better, but I'd be happy to submit this
as a proper patch, if this is more to your liking.

Thanks,
  Frank


> Maxime
>
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