[PATCH v3 1/2] powerpc/mm: Cleanup memory block size probing

[Reza Arbab]

On Fri, Jul 28, 2023 at 04:05:55PM +0530, Aneesh Kumar K.V wrote:
>--- a/arch/powerpc/mm/init_64.c
>+++ b/arch/powerpc/mm/init_64.c
[snip]
>+	/*
>+	 * "ibm,coherent-device-memory with linux,usable-memory = 0
>+	 * Force 256MiB block size. Work around for GPUs on P9 PowerNV
>+	 * linux,usable-memory == 0 implies driver managed memory and
>+	 * we can't use large memory block size due to hotplug/unplug
>+	 * limitations.
>+	 */
>+	compatible = of_get_flat_dt_prop(node, "compatible", NULL);
>+	if (compatible && !strcmp(compatible, "ibm,coherent-device-memory")) {
>+		int len = 0;
>+		const __be32 *usm;
>+
>+		usm = of_get_flat_dt_prop(node, "linux,drconf-usable-memory", &len);

I think this should be "linux,usable-memory".

>+		if (usm && !len) {
>+			*block_size = SZ_256M;
>+			return 1;
>+		}

This isn't quite right. The criteria is not that the property itself has 
no registers, it's that the base/size combo has size zero.

If you fold in the patch appended to the end of this mail, things worked 
for me.

>+	}
>+
>+	reg = of_get_flat_dt_prop(node, "reg", &l);
>+	endp = reg + (l / sizeof(__be32));
>+
>+	while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
>+		u64 base, size;
>+
>+		base = dt_mem_next_cell(dt_root_addr_cells, &reg);
>+		size = dt_mem_next_cell(dt_root_size_cells, &reg);
>+
>+		if (size == 0)
>+			continue;
>+
>+		update_memory_block_size(block_size, size);
>+	}
>+	/* continue looking for other memory device types */
>+	return 0;
>+}
>+
>+/*
>+ * start with 1G memory block size. Early init will
>+ * fix this with correct value.
>+ */
>+unsigned long memory_block_size __ro_after_init = 1UL << 30;

Could use SZ_1G here.

With the following fixup, I got 256MiB blocks on a system with
"ibm,coherent-device-memory" nodes.

diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index dbed37d6cffb..1ac58e72a885 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -487,7 +487,6 @@ static int __init probe_memory_block_size(unsigned long node, const char *uname,
  					  depth, void *data)
  {
  	const char *type;
-	const char *compatible;
  	unsigned long *block_size = (unsigned long *)data;
  	const __be32 *reg, *endp;
  	int l;
@@ -532,38 +531,38 @@ static int __init probe_memory_block_size(unsigned long node, const char *uname,
  	if (type == NULL || strcmp(type, "memory") != 0)
  		return 0;
  
-	/*
-	 * "ibm,coherent-device-memory with linux,usable-memory = 0
-	 * Force 256MiB block size. Work around for GPUs on P9 PowerNV
-	 * linux,usable-memory == 0 implies driver managed memory and
-	 * we can't use large memory block size due to hotplug/unplug
-	 * limitations.
-	 */
-	compatible = of_get_flat_dt_prop(node, "compatible", NULL);
-	if (compatible && !strcmp(compatible, "ibm,coherent-device-memory")) {
-		int len = 0;
-		const __be32 *usm;
-
-		usm = of_get_flat_dt_prop(node, "linux,drconf-usable-memory", &len);
-		if (usm && !len) {
-			*block_size = SZ_256M;
-			return 1;
-		}
-	}
+	reg = of_get_flat_dt_prop(node, "linux,usable-memory", &l);
+	if (!reg)
+		reg = of_get_flat_dt_prop(node, "reg", &l);
+	if (!reg)
+		return 0;
  
-	reg = of_get_flat_dt_prop(node, "reg", &l);
  	endp = reg + (l / sizeof(__be32));
  
  	while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
+		const char *compatible;
  		u64 base, size;
  
  		base = dt_mem_next_cell(dt_root_addr_cells, &reg);
  		size = dt_mem_next_cell(dt_root_size_cells, &reg);
  
-		if (size == 0)
+		if (size) {
+			update_memory_block_size(block_size, size);
  			continue;
+		}
  
-		update_memory_block_size(block_size, size);
+		/*
+		 * ibm,coherent-device-memory with linux,usable-memory = 0
+		 * Force 256MiB block size. Work around for GPUs on P9 PowerNV
+		 * linux,usable-memory == 0 implies driver managed memory and
+		 * we can't use large memory block size due to hotplug/unplug
+		 * limitations.
+		 */
+		compatible = of_get_flat_dt_prop(node, "compatible", NULL);
+		if (compatible && !strcmp(compatible, "ibm,coherent-device-memory")) {
+			*block_size = SZ_256M;
+			return 1;
+		}
  	}
  	/* continue looking for other memory device types */
  	return 0;
-- 
Reza Arbab