It is not sufficient to specify a minus sign in the device tree source. In this example, dtc will not warn that the two values 21474836483649 will be negative values on the target system. Notice how the integer values wrap from the most positive to the most negative, even though the unsigned 32 bit values are monotonically increasing. Will be 2's complement values on the target, if the kernel code properly interprets them as signed: In this example, the values from the device tree source file: Using signed property data values can lead to errors in device tree source files that the dtc compiler can not detect. How to represent negative values for device tree property The side effect of this is that negativeĬonstants must be enclosed in parenthesis, for example: (-327). However, recent versions of the dtc compiler do allow signed 32 bit object as data values,Īs a result of adding integer expression support. There is no mention of a signed data type. See this warning, W=3 has to be provided to the make command.ġ47 np = of_find_node_by_name(NULL, "node_xxx") ġ50 rc = of_property_read_u32(np, "a", &val) ġ54 rc = of_property_read_u32(np, "b", &val) ġ58 rc = of_property_read_u32(np, "c", &val) ġ62 rc = of_property_read_u32(np, "d", &val) ĭrivers/misc/xxx.c:151:2: warning: conversion to 'int' from 'u32' may change the sign of the result ĭrivers/misc/xxx.c:155:2: warning: conversion to 'int' from 'u32' may change the sign of the result ĭrivers/misc/xxx.c:159:2: warning: conversion to 'int' from 'u32' may change the sign of the result ĭrivers/misc/xxx.c:163:2: warning: conversion to 'int' from 'u32' may change the sign of the result ĭevice Tree source Signed Property ValuesĮPAPR Version 1.1 lists the following data types for properties: Will warn that there is a possible problem. Variable (as in the following example), then the compiler However, if the address of a u32 is passed to of_property_read_u32(),Īnd then the value of the u32 is assigned to an integer Instead of the address of a u32 was passed to of_property_read_u32(). There was no compiler warning that the address of an int This is because the integer variables treat the Property values, even though the device tree source contains only The console output from the example driver code shows some negative Np = of_find_node_by_name(NULL, "node_xxx") ĭevice tree source, providing values for the properties a, b, c, and d: (see Device Tree source : Signed Property ValuesĪ common incorrect pattern in Linux drivers is to read a u32 property value However, recent versions of the dtc compiler allow specifying negative values There is no signed data type for property values in device tree source files. 5 defaults and inheritance of #address-cells and #size-cellsĭevicetree: Kernel Internals and Practical Troubleshooting Ĭommon Linux Driver Errors Assign property value to a signed integer.3.10 Interrupt Nexus / Interrupt Mapping.3.6 Label as a phandle vs Label as a path.3.4 Labels on a property or a property value.2.1 Assign property value to a signed integer.1 device creation, driver binding, probing.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |