Re: [PATCH v13 5/6] drm/mediatek: dpi sample mode support

[Neil Armstrong <narmstrong@baylibre.com>]

On 11/03/2020 08:18, Jitao Shi wrote:
> DPI can sample on falling, rising or both edge.
> When DPI sample the data both rising and falling edge.
> It can reduce half data io pins.
> 
> Reviewed-by: CK Hu <ck.hu@mediatek.com>
> Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dpi.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
> index 087f5ce732e1..2871e68e7767 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
> @@ -75,6 +75,7 @@ struct mtk_dpi {
>  	enum mtk_dpi_out_bit_num bit_num;
>  	enum mtk_dpi_out_channel_swap channel_swap;
>  	int refcount;
> +	u32 pclk_sample;
>  };
>  
>  static inline struct mtk_dpi *mtk_dpi_from_encoder(struct drm_encoder *e)
> @@ -348,6 +349,13 @@ static void mtk_dpi_config_disable_edge(struct mtk_dpi *dpi)
>  		mtk_dpi_mask(dpi, dpi->conf->reg_h_fre_con, 0, EDGE_SEL_EN);
>  }
>  
> +static void mtk_dpi_enable_pclk_sample_dual_edge(struct mtk_dpi *dpi)
> +{
> +	mtk_dpi_mask(dpi, DPI_DDR_SETTING, DDR_EN | DDR_4PHASE,
> +		     DDR_EN | DDR_4PHASE);
> +	mtk_dpi_mask(dpi, DPI_OUTPUT_SETTING, EDGE_SEL, EDGE_SEL);
> +}
> +
>  static void mtk_dpi_config_color_format(struct mtk_dpi *dpi,
>  					enum mtk_dpi_out_color_format format)
>  {
> @@ -439,7 +447,8 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>  	pll_rate = clk_get_rate(dpi->tvd_clk);
>  
>  	vm.pixelclock = pll_rate / factor;
> -	clk_set_rate(dpi->pixel_clk, vm.pixelclock);
> +	clk_set_rate(dpi->pixel_clk,
> +		     vm.pixelclock * (dpi->pclk_sample > 1 ? 2 : 1));
>  	vm.pixelclock = clk_get_rate(dpi->pixel_clk);
>  
>  	dev_dbg(dpi->dev, "Got  PLL %lu Hz, pixel clock %lu Hz\n",
> @@ -450,7 +459,8 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>  	limit.y_bottom = 0x0010;
>  	limit.y_top = 0x0FE0;
>  
> -	dpi_pol.ck_pol = MTK_DPI_POLARITY_FALLING;
> +	dpi_pol.ck_pol = dpi->pclk_sample == 1 ?
> +			 MTK_DPI_POLARITY_RISING : MTK_DPI_POLARITY_FALLING;
>  	dpi_pol.de_pol = MTK_DPI_POLARITY_RISING;
>  	dpi_pol.hsync_pol = vm.flags & DISPLAY_FLAGS_HSYNC_HIGH ?
>  			    MTK_DPI_POLARITY_FALLING : MTK_DPI_POLARITY_RISING;
> @@ -504,6 +514,8 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>  	mtk_dpi_config_color_format(dpi, dpi->color_format);
>  	mtk_dpi_config_2n_h_fre(dpi);
>  	mtk_dpi_config_disable_edge(dpi);
> +	if (dpi->pclk_sample > 1)
> +		mtk_dpi_enable_pclk_sample_dual_edge(dpi);
>  	mtk_dpi_sw_reset(dpi, false);
>  
>  	return 0;
> @@ -693,6 +705,7 @@ static const struct mtk_dpi_conf mt8183_conf = {
>  static int mtk_dpi_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> +	struct device_node *ep;
>  	struct mtk_dpi *dpi;
>  	struct resource *mem;
>  	int comp_id;
> @@ -705,6 +718,16 @@ static int mtk_dpi_probe(struct platform_device *pdev)
>  	dpi->dev = dev;
>  	dpi->conf = (struct mtk_dpi_conf *)of_device_get_match_data(dev);
>  
> +	ep = of_graph_get_endpoint_by_regs(dev->of_node, 0, 0);
> +	if (!ep) {
> +		dev_err(dev, "Failed get the endpoint port\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Get the sampling edge from the endpoint. */
> +	of_property_read_u32(ep, "pclk-sample", &dpi->pclk_sample);
> +	of_node_put(ep);

Instead of having hard-coded value in DT, you should switch to bridge bus
format negotiation instead.

Boris pushed support a few weeks ago and the dw-hdmi bridge has been updated
to work with it and negotiate the format between the encoder and the bridge.

Phong is pushing the it66121 bridge driver which is used on a MT8183 board, and
should make use of that to handle the dual edge support between the 8183 dpi and
the it66121 bridge.

Neil

> +
>  	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>  	dpi->regs = devm_ioremap_resource(dev, mem);
>  	if (IS_ERR(dpi->regs)) {
>