On Wed 05 Aug 09:32 PDT 2015, Lina Iyer wrote: > Hwspinlocks are widely used between processors in an SoC, and also > between elevation levels within in the same processor. QCOM SoC's use > hwspinlock to serialize entry into a low power mode when the context > switches from Linux to secure monitor. > > Lock #7 has been assigned for this purpose. In order to differentiate > between one cpu core holding a lock while another cpu is contending for > the same lock, the proc id written into the lock is (128 + cpu id). This > makes it unique value among the cpu cores and therefore when a core > locks the hwspinlock, other cores would wait for the lock to be released > since they would have a different proc id. This value is specific for > the lock #7 only. > As I was thinking about this, I came to the conclusion that my argument that it's system configuration and not a property of the block that lock #7 is special is actually biting myself. Just as #7 is system configuration, so is the fact that 1 is the lock value for all other locks. I've been meaning to answer you, but I haven't come to a good conclusion in this matter. I think that both of these properties should be possible to express in DT, but I don't know how. Perhaps we should just list each lock that we expose as a subnode in DT with a property to indicate the lock value - with the possibility of indicating cpu_id. Something like: tcsr-mutex { compatible = "qcom,tcsr-mutex"; syscon = <&tcsr_mutex_block 0 0x80>; #hwlock-cells = <1>; #address-cells = <1>; #size-cells = <0>; smem-lock@3 { reg = <3>; qcom,lock-value = <1>; }; scm-lock@7 { reg = <7>; qcom,lock-value-from-cpu-id; qcom,lock-raw; }; }; As we don't reference most of these locks anyways I don't think this would still be reasonable. And if reg is an array it's quite compact. > Declare lock #7 as raw capable, so the hwspinlock framework would not > enfore acquiring a s/w spinlock before acquiring the hwspinlock. > I'm fine with this part! Sorry for the extremely slow response, but this took some time to process... Regards, Bjorn -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html