[POWERPC] Donate idle CPU cycles on dedicated partitions

A Power6 can give up CPU cycles on a dedicated CPU (as opposed to a
shared CPU) to other shared processors if the administrator asks for it
(via the HMC).

This enables that to work properly on P6.

This just involves setting a bit in the CAS structure as well as the
VPA.  To donate cycles, a CPU has to have all SMT threads idle and
have the donate bit set in the VPA.  Then call H_CEDE.

The reason why shared processors just aren't used is because dedicated
CPUs are guaranteed an actual processor, yet the system is still able to
increase the capacity of the shared CPU pool.

Also rename the VPA's cpuctls_task_attrs field to a more accurate name.
Signed-off-by: Jake Moilanen <moilanen@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/prom_init.c

@@ -635,6 +635,7 @@ static void __init early_cmdline_parse(void)
 /* ibm,dynamic-reconfiguration-memory property supported */
 #define OV5_DRCONF_MEMORY	0x20
 #define OV5_LARGE_PAGES		0x10	/* large pages supported */
+#define OV5_DONATE_DEDICATE_CPU 0x02	/* donate dedicated CPU support */
 /* PCIe/MSI support.  Without MSI full PCIe is not supported */
 #ifdef CONFIG_PCI_MSI
 #define OV5_MSI			0x01	/* PCIe/MSI support */
@@ -685,7 +686,8 @@ static unsigned char ibm_architecture_vec[] = {
 	/* option vector 5: PAPR/OF options */
 	3 - 2,				/* length */
 	0,				/* don't ignore, don't halt */
-	OV5_LPAR | OV5_SPLPAR | OV5_LARGE_PAGES | OV5_DRCONF_MEMORY | OV5_MSI,
+	OV5_LPAR | OV5_SPLPAR | OV5_LARGE_PAGES | OV5_DRCONF_MEMORY |
+	OV5_DONATE_DEDICATE_CPU | OV5_MSI,
 };
 
 /* Old method - ELF header with PT_NOTE sections */

arch/powerpc/platforms/pseries/setup.c

@@ -399,6 +399,7 @@ static void pseries_dedicated_idle_sleep(void)
 	 * a good time to find other work to dispatch.
 	 */
 	get_lppaca()->idle = 1;
+	get_lppaca()->donate_dedicated_cpu = 1;
 
 	/*
 	 * We come in with interrupts disabled, and need_resched()
@@ -431,6 +432,7 @@ static void pseries_dedicated_idle_sleep(void)
 
 out:
 	HMT_medium();
+	get_lppaca()->donate_dedicated_cpu = 0;
 	get_lppaca()->idle = 0;
 }
 

include/asm-powerpc/lppaca.h

@@ -98,7 +98,7 @@ struct lppaca {
 	u64	saved_gpr5;		// Saved GPR5                   x30-x37
 
 	u8	reserved4;		// Reserved			x38-x38
-	u8	cpuctls_task_attrs;	// Task attributes for cpuctls  x39-x39
+	u8	donate_dedicated_cpu;	// Donate dedicated CPU cycles  x39-x39
 	u8	fpregs_in_use;		// FP regs in use               x3A-x3A
 	u8	pmcregs_in_use;		// PMC regs in use              x3B-x3B
 	volatile u32 saved_decr;	// Saved Decr Value             x3C-x3F