powerpc/vas: Define QoS credit flag to allocate window

PowerVM introduces two different type of credits: Default and Quality
of service (QoS).

The total number of default credits available on each LPAR depends
on CPU resources configured. But these credits can be shared or
over-committed across LPARs in shared mode which can result in
paste command failure (RMA_busy). To avoid NX HW contention, the
hypervisor ntroduces QoS credit type which makes sure guaranteed
access to NX esources. The system admins can assign QoS credits
or each LPAR via HMC.

Default credit type is used to allocate a VAS window by default as
on PowerVM implementation. But the process can pass
VAS_TX_WIN_FLAG_QOS_CREDIT flag with VAS_TX_WIN_OPEN ioctl to open
QoS type window.
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/aa950b7b8e8077364267720274a7b9ec34e76e73.camel@linux.ibm.com

arch/powerpc/include/uapi/asm/vas-api.h

@@ -13,11 +13,15 @@
 #define VAS_MAGIC	'v'
 #define VAS_TX_WIN_OPEN	_IOW(VAS_MAGIC, 0x20, struct vas_tx_win_open_attr)
 
+/* Flags to VAS TX open window ioctl */
+/* To allocate a window with QoS credit, otherwise use default credit */
+#define VAS_TX_WIN_FLAG_QOS_CREDIT	0x0000000000000001
+
 struct vas_tx_win_open_attr {
 	__u32	version;
 	__s16	vas_id;	/* specific instance of vas or -1 for default */
 	__u16	reserved1;
-	__u64	flags;	/* Future use */
+	__u64	flags;
 	__u64	reserved2[6];
 };