Comment 17 for bug 392812

Commenting out the goto end; line in acpi_ec_transaction and recompiling the kernel from source works around the bug for me -- I still get the "input buffer not empty" error messages in dmesg, but the brightness keys and AC adapter detection continue to work.

static int acpi_ec_transaction(struct acpi_ec *ec, struct transaction *t,
                               int force_poll)
{
        int status;
        u32 glk;
        if (!ec || (!t) || (t->wlen && !t->wdata) || (t->rlen && !t->rdata))
                return -EINVAL;
        if (t->rdata)
                memset(t->rdata, 0, t->rlen);
        mutex_lock(&ec->lock);
        if (ec->global_lock) {
                status = acpi_acquire_global_lock(ACPI_EC_UDELAY_GLK, &glk);
                if (ACPI_FAILURE(status)) {
                        status = -ENODEV;
                        goto unlock;
                }
        }
        if (ec_wait_ibf0(ec)) {
                pr_err(PREFIX "input buffer is not empty, "
                                "aborting transaction--\n");
                status = -ETIME;
                //goto end;

        }
        status = acpi_ec_transaction_unlocked(ec, t, force_poll);
end:
        if (ec->global_lock)
                acpi_release_global_lock(glk);
unlock:
        mutex_unlock(&ec->lock);
        return status;
}