powerpc/rtas: improve function information lookups
The core RTAS support code and its clients perform two types of lookup for RTAS firmware function information. First, mapping a known function name to a token. The typical use case invokes rtas_token() to retrieve the token value to pass to rtas_call(). rtas_token() relies on of_get_property(), which performs a linear search of the /rtas node's property list under a lock with IRQs disabled. Second, and less common: given a token value, looking up some information about the function. The primary example is the sys_rtas filter path, which linearly scans a small table to match the token to a rtas_filter struct. Another use case to come is RTAS entry/exit tracepoints, which will require efficient lookup of function names from token values. Currently there is no general API for this. We need something much like the existing rtas_filters table, but more general and organized to facilitate efficient lookups. Introduce: * A new rtas_function type, aggregating function name, token, and filter. Other function characteristics could be added in the future. * An array of rtas_function, where each element corresponds to a known RTAS function. All information in the table is static save the token values, which are derived from the device tree at boot. The array is sorted by function name to allow binary search. * A named constant for each known RTAS function, used to index the function array. These also will be used in a client-facing API to be added later. * An xarray that maps valid tokens to rtas_function objects. Fold the existing rtas_filter table into the new rtas_function array, with the appropriate adjustments to block_rtas_call(). Remove now-redundant fields from struct rtas_filter. Preserve the function of the CONFIG_CPU_BIG_ENDIAN guard in the current filter table by introducing a per-function flag that is set for the function entries related to pseries LPAR migration. These have never had working users via sys_rtas on ppc64le; see commit de0f7349 ("powerpc/rtas: prevent suspend-related sys_rtas use on LE"). Convert rtas_token() to use a lockless binary search on the function table. Fall back to the old behavior for lookups against names that are not known to be RTAS functions, but issue a warning. rtas_token() is for function names; it is not a general facility for accessing arbitrary properties of the /rtas node. All known misuses of rtas_token() have been converted to more appropriate of_ APIs in preceding changes. Signed-off-by:Nathan Lynch <nathanl@linux.ibm.com> Signed-off-by: