[PATCH RFC] l2c: warn about misconfigured PL310 shared-override

[Lucas Stach]

If the shared override enable bit in the PL310 aux ctrl register is
not set the L2 cache controller will render the system non-compliant
to the rules regarding mismatched memory aliases as specified in the
ARMv7 ARM.

As this may lead to subtle corruptions when reading from a bufferable
alias, make sure to warn about this in the kernel log.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
I'm open to suggestions on how to improve the warning or where to put
documentation for this so users are advised to update their board
firmware, or work around this by using the "arm,shared-override" DT
property on a secure state booted kernel, without spamming the logs
too much.
---
 arch/arm/mm/cache-l2x0.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
index 493692d838c6..8c586894c58d 100644
--- a/arch/arm/mm/cache-l2x0.c
+++ b/arch/arm/mm/cache-l2x0.c
@@ -820,6 +820,11 @@ static int __init __l2c_init(const struct l2c_init_data *data,
 		pr_warn("L2C: DT/platform modifies aux control register: 0x%08x -> 0x%08x\n",
 		        old_aux, aux);
 
+	if (((cache_id & L2X0_CACHE_ID_PART_MASK) == L2X0_CACHE_ID_PART_L310) &&
+	    !(aux & L2C_AUX_CTRL_SHARED_OVERRIDE))
+		pr_warn("L2C-310 shared attribute override enable not set, "
+			"system is non-compliant to ARM specified memory aliasing rules\n");
+
 	/* Determine the number of ways */
 	switch (cache_id & L2X0_CACHE_ID_PART_MASK) {
 	case L2X0_CACHE_ID_PART_L310:
-- 
2.6.1