Subject: Re: [PATCH 2/2] powerpc/pseries: Dynamically increase RMA size

From: Sukadev Bhattiprolu <[email-masked]>
Date: Fri, 5 Aug 2016 11:30:55 -0700

Here is an updated patch to fix the build when CONFIG_PPC_PSERIES=n.
---
>>From d4f77a6ca7b6ea83f6588e7d541cc70bf001ae85 Mon Sep 17 00:00:00 2001
From: root <[email-masked]>
Date: Thu, 4 Aug 2016 23:13:37 -0400
Subject: [PATCH 2/2] powerpc/pseries: Dynamically grow RMA size

When booting a very large system with a larg initrd we run out of space
for the flattened device tree (FDT). To fix this we must increase the
space allocated for the RMA region.

The RMA size is hard-coded in the 'ibm_architecture_vec[]' and increasing
the size there will apply to all systems, small and large, so we want to
increase the RMA region only when necessary.

When we run out of room for the FDT, set a new OF property, 'ibm,new-rma-size'
to the new RMA size (512MB) and issue a client-architecture-support (CAS)
call to the firmware. This will initiate a system reboot. Upon reboot we
notice the new property and update the RMA size accordingly.

Fix suggested by Michael Ellerman.

Signed-off-by: Sukadev Bhattiprolu <[email-masked]>
---

[v2]:	- Add a comment in code regarding 'fixup_nr_cores_done'
	- Fix build break when CONFIG_PPC_PSERIES=n
---
 arch/powerpc/kernel/prom_init.c | 96 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index f612a99..cbd5387 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -679,6 +679,7 @@ unsigned char ibm_architecture_vec[] = {
 	W(0xffffffff),			/* virt_base */
 	W(0xffffffff),			/* virt_size */
 	W(0xffffffff),			/* load_base */
+#define IBM_ARCH_VEC_MIN_RMA_OFFSET	108
 	W(256),				/* 256MB min RMA */
 	W(0xffffffff),			/* full client load */
 	0,				/* min RMA percentage of total RAM */
@@ -867,6 +868,14 @@ static void fixup_nr_cores(void)
 {
 	u32 cores;
 	unsigned char *ptcores;
+	static bool fixup_nr_cores_done = false;
+
+	/*
+	 * If this is a second CAS call in the same boot sequence, (see
+	 * increase_rma_size()), we don't need to do the fixup again.
+	 */
+	if (fixup_nr_cores_done)
+		return;
 
 	/* We need to tell the FW about the number of cores we support.
 	 *
@@ -898,6 +907,41 @@ static void fixup_nr_cores(void)
 		ptcores[1] = (cores >> 16) & 0xff;
 		ptcores[2] = (cores >> 8) & 0xff;
 		ptcores[3] = cores & 0xff;
+		fixup_nr_cores_done = true;
+	}
+}
+
+static void __init fixup_rma_size(void)
+{
+	int rc;
+	u64 size;
+	unsigned char *min_rmap;
+	phandle optnode;
+	char str[64];
+
+	optnode = call_prom("finddevice", 1, 1, ADDR("/options"));
+	if (!PHANDLE_VALID(optnode))
+		prom_panic("Cannot find /options");
+
+	/*
+	 * If a prior boot specified a new RMA size, use that size in
+	 * ibm_architecture_vec[]. See also increase_rma_size().
+	 */
+	size = 0ULL;
+	memset(str, 0, sizeof(str));
+	rc = prom_getprop(optnode, "ibm,new-rma-size", &str, sizeof(str));
+	if (rc <= 0)
+		return;
+
+	size = prom_strtoul(str, NULL);
+	min_rmap = &ibm_architecture_vec[IBM_ARCH_VEC_MIN_RMA_OFFSET];
+
+	if (size) {
+		prom_printf("Using RMA size %lu from ibm,new-rma-size.\n", size);
+		min_rmap[0] = (size >> 24) & 0xff;
+		min_rmap[1] = (size >> 16) & 0xff;
+		min_rmap[2] = (size >> 8) & 0xff;
+		min_rmap[3] = size & 0xff;
 	}
 }
 
@@ -911,6 +955,8 @@ static void __init prom_send_capabilities(void)
 
 		fixup_nr_cores();
 
+		fixup_rma_size();
+
 		/* try calling the ibm,client-architecture-support method */
 		prom_printf("Calling ibm,client-architecture-support...");
 		if (call_prom_ret("call-method", 3, 2, &ret,
@@ -946,6 +992,52 @@ static void __init prom_send_capabilities(void)
 	}
 #endif /* __BIG_ENDIAN__ */
 }
+
+static void __init increase_rma_size(void)
+{
+	int rc;
+	u64 size;
+	char str[64];
+	phandle optnode;
+
+	optnode = call_prom("finddevice", 1, 1, ADDR("/options"));
+	if (!PHANDLE_VALID(optnode))
+		prom_panic("Cannot find /options");
+
+	/*
+	 * If we already increased the RMA size, return.
+	 */
+	size = 0ULL;
+	memset(str, 0, sizeof(str));
+	rc = prom_getprop(optnode, "ibm,new-rma-size", &str, sizeof(str));
+
+	size = prom_strtoul(str, NULL);
+	if (size == 512ULL) {
+		prom_printf("RMA size already at %lu.\n", size);
+		return;
+	}
+	/*
+	 * Otherwise, set the ibm,new-rma-size property and initiate a CAS
+	 * reboot so the RMA size can take effect. See also init_rma_size().
+	 */
+	memset(str, 0, 4);
+	memcpy(str, "512", 3);
+	prom_printf("Setting ibm,new-rma-size property to %s\n", str);
+	rc = prom_setprop(optnode, "/options", "ibm,new-rma-size", &str,
+					strlen(str)+1);
+
+	/* Force a reboot. Will work only if ibm,fw-override-cas==false */
+	prom_send_capabilities();
+
+	prom_printf("No CAS initiated reboot? Try setting ibm,fw-override-cas to 'false' in Open Firmware\n");
+}
+
+#else
+
+static void __init increase_rma_size(void)
+{
+}
+
 #endif /* #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_PPC_POWERNV) */
 
 /*
@@ -2027,9 +2119,11 @@ static void __init *make_room(unsigned long *mem_start, unsigned long *mem_end,
 		room = alloc_top - alloc_bottom;
 		if (room > DEVTREE_CHUNK_SIZE)
 			room = DEVTREE_CHUNK_SIZE;
-		if (room < PAGE_SIZE)
+		if (room < PAGE_SIZE) {
+			increase_rma_size();
 			prom_panic("No memory for flatten_device_tree "
 				   "(no room)\n");
+		}
 		chunk = alloc_up(room, 0);
 		if (chunk == 0)
 			prom_panic("No memory for flatten_device_tree "
-- 
1.8.3.1