ARM platforms: rationalise memory attributes of shared memory
The shared memory region on ARM platforms contains the mailboxes and,
on Juno, the payload area for communication with the SCP. This shared
memory may be configured as normal memory or device memory at build
time by setting the platform flag 'PLAT_ARM_SHARED_RAM_CACHED' (on
Juno, the value of this flag is defined by 'MHU_PAYLOAD_CACHED').
When set as normal memory, the platform port performs the corresponding
cache maintenance operations. From a functional point of view, this is
the equivalent of setting the shared memory as device memory, so there
is no need to maintain both options.
This patch removes the option to specify the shared memory as normal
memory on ARM platforms. Shared memory is always treated as device
memory. Cache maintenance operations are no longer needed and have
been replaced by data memory barriers to guarantee that payload and
MHU are accessed in the right order.
Change-Id: I7f958621d6a536dd4f0fa8768385eedc4295e79f
diff --git a/plat/arm/css/common/css_scp_bootloader.c b/plat/arm/css/common/css_scp_bootloader.c
index c01f42f..4367459 100644
--- a/plat/arm/css/common/css_scp_bootloader.c
+++ b/plat/arm/css/common/css_scp_bootloader.c
@@ -77,10 +77,10 @@
static void scp_boot_message_send(size_t payload_size)
{
- /* Make sure payload can be seen by SCP */
- if (MHU_PAYLOAD_CACHED)
- flush_dcache_range(BOM_SHARED_MEM,
- sizeof(bom_cmd_t) + payload_size);
+ /* Ensure that any write to the BOM payload area is seen by SCP before
+ * we write to the MHU register. If these 2 writes were reordered by
+ * the CPU then SCP would read stale payload data */
+ dmbst();
/* Send command to SCP */
mhu_secure_message_send(BOM_MHU_SLOT_ID);
@@ -99,9 +99,10 @@
panic();
}
- /* Make sure we see the reply from the SCP and not any stale data */
- if (MHU_PAYLOAD_CACHED)
- inv_dcache_range(BOM_SHARED_MEM, size);
+ /* Ensure that any read to the BOM payload area is done after reading
+ * the MHU register. If these 2 reads were reordered then the CPU would
+ * read invalid payload data */
+ dmbld();
return *(uint32_t *) BOM_SHARED_MEM;
}