On 01/14/2014 07:45 AM, Thierry Reding wrote:
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.
The series, Tested-by: Stephen Warren swarren@nvidia.com
This patch should really have been sent to the DT maintainers and list since it changes a DT binding...
diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
+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 of_property_read_u32() returns an error, does it guarantee that value is left unchanged? I suspect it'd be safer to add ...
- 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.*/
... "value = 0;" here?
for_each_matching_node(np, tegra_dc_of_match) {if (np == dc->dev->of_node)break;value++;}- }
- dc->pipe = value;