On 12/01/2011 06:01 PM, Simon Glass wrote:
Hi Stephen,
On Mon, Nov 28, 2011 at 10:41 AM, Stephen Warren swarren@nvidia.com wrote:
On 11/23/2011 08:54 PM, Simon Glass wrote:
Add a function to lookup a property which is a phandle in a node, and another to read a fixed-length integer array from an fdt property. Also add a function to read boolean properties.
Signed-off-by: Simon Glass sjg@chromium.org
+/**
- Look up a boolean property in a node and return it.
- A boolean properly is true if present in the device tree and false if not
- present, or present with a 0 value.
- @param blob FDT blob
- @param node node to examine
- @param prop_name name of property to find
- @return 1 if the properly is present; 0 if it isn't present or is 0
- */
+int fdtdec_get_bool(const void *blob, int node, const char *prop_name);
Does U-Boot allow use of the "bool" type here?
Which bool type? It is returning an int.
I was asking if the return type could be changed to bool.
+int fdtdec_get_bool(const void *blob, int node, const char *prop_name) +{
const s32 *cell;int len;debug("%s: %s\n", __func__, prop_name);cell = fdt_getprop(blob, node, prop_name, &len);if (!cell)return 0;if (len >= sizeof(u32) && *cell == 0)return 0;return 1;+}
In the kernel, I believe that property existence is all that's usually checked. Is that wrong? Did the definition of a boolean property's value in the function description above come from the specification? If a property had a length of 0/1/2/3 with a zero value, it seems very odd to treat that as true.
It is useful to be able to set the value to 0 or 1 (with fdtget/put), rather than remove or add the property. A value with a length of less than one cell is considered illegal here.
The basic idea is that the presence of the property means that it is 'true'. If it happens to have a value, then we allow that to specify 'false' if it is zero.
Well, it's more up to standard device tree practice, not me. I've certainly sent patches that used a property with 0/1 value as a bool and received review feedback from DT experts that DT represents bools as present/absent properties, both with no value, so I assume zero length.