powerpc/rtas: improve ppc_rtas_rmo_buf_show documentation

Add kerneldoc for ppc_rtas_rmo_buf_show(), the callback for
/proc/powerpc/rtas/rmo_buffer, explaining its expected use.

Signed-off-by: Nathan Lynch <[email protected]>
Reviewed-by: Alexey Kardashevskiy <[email protected]>
Reviewed-by: Andrew Donnellan <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/rtas-proc.c b/arch/powerpc/kernel/rtas-proc.c
index 2d33f342a293..e0f8329966d6 100644
--- a/arch/powerpc/kernel/rtas-proc.c
+++ b/arch/powerpc/kernel/rtas-proc.c
@@ -757,7 +757,16 @@ static int ppc_rtas_tone_volume_show(struct seq_file *m, void *v)
 
 #define RMO_READ_BUF_MAX 30
 
-/* RTAS Userspace access */
+/**
+ * ppc_rtas_rmo_buf_show() - Describe RTAS-addressable region for user space.
+ *
+ * Base + size description of a range of RTAS-addressable memory set
+ * aside for user space to use as work area(s) for certain RTAS
+ * functions. User space accesses this region via /dev/mem. Apart from
+ * security policies, the kernel does not arbitrate or serialize
+ * access to this region, and user space must ensure that concurrent
+ * users do not interfere with each other.
+ */
 static int ppc_rtas_rmo_buf_show(struct seq_file *m, void *v)
 {
 	seq_printf(m, "%016lx %x\n", rtas_rmo_buf, RTAS_RMOBUF_MAX);