On Thu, Nov 10, 2016 at 09:55:16PM +0100, Julia Lawall wrote: > As far as I can see in the various definitions of clk_get_parent, they all > return either NULL or a value stored in a structure field. But the > documentation with the prototype in includ/linux/clk.h says that it > returns a valid IS_ERR() condition containing errno. Are ERR_PTR values > stored in the structure fields?
The API documentation (in clk.h) is correct. The API (from the user perspective) considers invalid clocks to be the set of pointers for which IS_ERR() is true. By implication, valid clocks are those for which IS_ERR() returns false. Hence, in order for clk_get_parent() to indicate an error, it has to return a pointer value which corresponds with IS_ERR() being true. The question over the NULL clock pointer is left to the implementation to decide whether it's an error or not as far as the API design goes, but practically everyone treats it as "there is no clock" which is entirely reasonable. Also, remember from the clk API design point of view, users of the API should never dereference the clk pointer, it is a cookie as far as users should be concerned. (The clk structure was not available to drivers in the early days.) Only clk implementations and clk drivers should dereference, and these should not dereference anything but their own clocks. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
