On 09/05/23 19:06, Krzysztof Kozlowski wrote:
External email: Use caution opening links or attachments
On 09/05/2023 15:17, Sumit Gupta wrote:
+ /*
+ * MC driver probe can't get BPMP reference as
it gets probed
+ * earlier than BPMP. So, save the BPMP ref got
from the EMC
+ * DT node in the mc->bpmp and use it in MC's
icc_set hook.
+ */
+ mc->bpmp = emc->bpmp;
This (and ()) are called without any locking. You register first the
interconnect, so set() callback can be used, right? Then set() could be
called anytime between tegra_emc_interconnect_init() and assignment
above. How do you synchronize these?
Best regards,
Krzysztof
Currently, the tegra234_mc_icc_set() has NULL check. So, it will give
this error.
if (!mc->bpmp) {
How does it solve concurrent accesses and re-ordering of instructions by
compiler or CPU?
Now, the "mc->bpmp" is set before tegra_emc_interconnect_init().
So, until the EMC interconnect initializes, set() won't be
called as the devm_of_icc_get() call will fail.
What if compiler puts "mc->bpmp" assignment after
tegra_emc_interconnect_init()?
What if CPU executes above assignment also after
tegra_emc_interconnect_init()?
Considering amount of code inside tegra_emc_interconnect_init() second
case is rather unlikely, but first possible, right?
Best regards,
Krzysztof
Yes, for protection from compiler re-ordering I can add
barrier() after the assignment.
mc->bpmp = emc->bpmp;
barrier();
Thank you,
Sumit Gupta
