On Tue, Aug 14, 2018 at 03:17:35PM -0700, Michal Wnukowski wrote:
> /* Update dbbuf and return true if an MMIO is required */
> static bool nvme_dbbuf_update_and_check_event(u16 value, u32 *dbbuf_db,
> - volatile u32 *dbbuf_ei)
> + u32 *dbbuf_ei)
> {
> if (dbbuf_db) {
> u16 old_value;
> @@ -306,6 +306,12 @@ static bool nvme_dbbuf_update_and_check_event(u16 value,
> u32 *dbbuf_db,
> old_value = *dbbuf_db;
> *dbbuf_db = value;
>
> + /*
> + * Ensure that the doorbell is updated before reading
> + * the EventIdx from memory
> + */
> + mb();
> +
> if (!nvme_dbbuf_need_event(*dbbuf_ei, value, old_value))
> return false;
> }
You just want to ensure the '*dbbuf_db = value' isn't reordered, right?
The order dependency might be more obvious if done as:
WRITE_ONCE(*dbbuf_db, value);
if (!nvme_dbbuf_need_event(READ_ONCE(*dbbuf_ei), value, old_value))
return false;
And 'volatile' is again redundant.
