On Tue, Jan 14, 2014 at 10:53:19AM -0700, Stephen Warren wrote:
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...
Indeed. I'll resend this to the appropriate people and lists. Sorry about that.
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 ...
That's the way it's always been at least. of_property_read_u32() ends up calling of_property_read_u32_array(), which looking at the code only modifies the out_values parameter when it knows that it will succeed.
Furthermore the function's kernel-doc explicitly says that "out_values is modified only if a valid u32 value can be decoded" (i.e. on success).
Thierry