[coreboot] Rowhammer DRAM Refresh

[Arthur Heymans]

Philipp Stanner <stanner at posteo.de> writes:

> Hi,
>
> where (which code file) does coreboot set the DRAM-refresh-rate and
> how easy is it for me to change it?

That would be in raminit, which is platform specific. So it depends on
readability of that code whether it's easy to find or not.

Not sure of this is possible with raminits like FSP or MRC.bin provided
in binary only.

>
> A higher refresh rate will decrease the performance but increase the
> protection against Rowhammer.
>
> // Philipp


Some example of how to achieve this on Intel 945 northbridge:

diff --git a/src/northbridge/intel/i945/raminit.c b/src/northbridge/intel/i945/raminit.c
index b5cce9c429..36dd601fb2 100644
--- a/src/northbridge/intel/i945/raminit.c
+++ b/src/northbridge/intel/i945/raminit.c
@@ -811,32 +811,8 @@ static void sdram_detect_smallest_refresh(struct sys_info * sysinfo)
 {
 	int i;
 
-	sysinfo->refresh = 0;
+	sysinfo->refresh = 1;
 
-	for (i = 0; i < 2*DIMM_SOCKETS; i++) {
-		int refresh;
-
-		if (sysinfo->dimm[i] == SYSINFO_DIMM_NOT_POPULATED)
-			continue;
-
-		refresh = spd_read_byte(get_dimm_spd_address(sysinfo, i),
-					SPD_REFRESH) & ~(1 << 7);
-
-		/* 15.6us */
-		if (!refresh)
-			continue;
-
-		/* Refresh is slower than 15.6us, use 15.6us */
-		if (refresh > 2)
-			continue;
-
-		if (refresh == 2) {
-			sysinfo->refresh = 1;
-			break;
-		}
-
-		die("DDR-II module has unsupported refresh value\n");
-	}
 	printk(BIOS_DEBUG, "Refresh: %s\n", sysinfo->refresh?"7.8us":"15.6us");
 }
 
 

-- 
Arthur Heymans