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Commit 13411ddd authored by Thierry Reding's avatar Thierry Reding
Browse files

drm/tegra: Obtain head number from DT 



The head number of a given display controller is fixed in hardware and
required to program outputs appropriately. Relying on the driver probe
order to determine this number will not work, since that could yield a
situation where the second head was probed first and would be assigned
head number 0 instead of 1.

By explicitly specifying the head number in the device tree, it is no
longer necessary to rely on these assumptions. As a fallback, if the
property isn't available, derive the head number from the display
controller node's position in the device tree. That's somewhat more
reliable than the previous default but not a proper solution.

Tested-by: default avatarStephen Warren <swarren@nvidia.com>
Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
parent 70bf6878

Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt

+3 −0
Original line number Diff line number Diff line
@@ -118,6 +118,9 @@ of the following host1x client modules: 
    See ../reset/reset.txt for details.

  - reset-names: Must include the following entries:

    - dc

  - nvidia,head: The number of the display controller head. This is used to

    setup the various types of output to receive video data from the given

    head.



  Each display controller node has a child node, named "rgb", that represents

  the RGB output associated with the controller. It can take the following

drivers/gpu/drm/tegra/dc.c

+39 −2
Original line number Diff line number Diff line
@@ -1100,8 +1100,6 @@ static int tegra_dc_init(struct host1x_client *client) 
	struct tegra_dc *dc = host1x_client_to_dc(client);

	int err;



	dc->pipe = tegra->drm->mode_config.num_crtc;



	drm_crtc_init(tegra->drm, &dc->base, &tegra_crtc_funcs);

	drm_mode_crtc_set_gamma_size(&dc->base, 256);

	drm_crtc_helper_add(&dc->base, &tegra_crtc_helper_funcs);
@@ -1187,6 +1185,41 @@ static const struct of_device_id tegra_dc_of_match[] = { 
	}

};



static int tegra_dc_parse_dt(struct tegra_dc *dc)

{

	struct device_node *np;

	u32 value = 0;

	int err;



	err = of_property_read_u32(dc->dev->of_node, "nvidia,head", &value);

	if (err < 0) {

		dev_err(dc->dev, "missing \"nvidia,head\" property\n");



		/*

		 * If the nvidia,head property isn't present, try to find the

		 * correct head number by looking up the position of this

		 * display controller's node within the device tree. Assuming

		 * that the nodes are ordered properly in the DTS file and

		 * that the translation into a flattened device tree blob

		 * preserves that ordering this will actually yield the right

		 * head number.

		 *

		 * If those assumptions don't hold, this will still work for

		 * cases where only a single display controller is used.

		 */

		for_each_matching_node(np, tegra_dc_of_match) {

			if (np == dc->dev->of_node)

				break;



			value++;

		}

	}



	dc->pipe = value;



	return 0;

}



static int tegra_dc_probe(struct platform_device *pdev)

{

	const struct of_device_id *id;
@@ -1207,6 +1240,10 @@ static int tegra_dc_probe(struct platform_device *pdev) 
	dc->dev = &pdev->dev;

	dc->soc = id->data;



	err = tegra_dc_parse_dt(dc);

	if (err < 0)

		return err;



	dc->clk = devm_clk_get(&pdev->dev, NULL);

	if (IS_ERR(dc->clk)) {

		dev_err(&pdev->dev, "failed to get clock\n");