On 31/10/14 06:41, Stephen Boyd wrote:
> On 10/30, Daniel Thompson wrote:
>> On 29/10/14 18:14, Stephen Boyd wrote:
>>> + r_count = min_t(int, count, sizeof(buf));
>>> +
>>> + for (i = 0; i < r_count; i++) {
>>> + char flag = TTY_NORMAL;
>>>
>>> - /* TODO: handle sysrq */
>>> - tty_insert_flip_string(tport, buf, min(count, 4));
>>> - count -= 4;
>>> + if (msm_port->break_detected && buf[i] == 0) {
>>> + port->icount.brk++;
>>> + flag = TTY_BREAK;
>>> + msm_port->break_detected = false;
>>> + if (uart_handle_break(port))
>>> + continue;
>>> + }
>>> +
>>> + if (!(port->read_status_mask & UART_SR_RX_BREAK))
>>> + flag = TTY_NORMAL;
>>
>> flag is already known to be TTY_NORMAL.
>
> Huh? If we detected a break we would set the flag to TTY_BREAK
> and if uart_handle_break() returned 0 (perhaps sysrq config is
> diasbled) then we would get down here, and then we want to reset
> the flag to TTY_NORMAL if the read_status_mask bits indicate that
> we want to skip checking for breaks. Otherwise we want to
> indicate to the tty layer that it's a break character.
Agreed. Sorry for noise.
It now reaches the level of silly quibble (meaning I won't bother to
raise the issue again if there is a v2 patch) but perhaps updating the
flag after the continue would be easier to read.
>>> +
>>> + spin_unlock(&port->lock);
>>
>> Is it safe to unlock at this point? count may no longer be valid when we
>> return.
>
> Can you explain further? If it actually isn't valid something
> needs to be done. I believe other serial drivers are doing this
> sort of thing though so it doesn't seem that uncommon (of course
> those drivers could also be broken I suppose).
Calling spin_unlock() means we are allow code to alter the state of the
UART. In particular the subsequent call to uart_handle_sysrq_char() can
make significant changes to the FIFO state (by calling the poll_char
functions). Given count is shadowing the FIFO state, when we retake the
lock I think it is possible for count to no longer be valid.
>
>>
>>
>>> + sysrq = uart_handle_sysrq_char(port, buf[i]);
>>> + spin_lock(&port->lock);
>>> + if (!sysrq)
>>> + tty_insert_flip_char(tport, buf[i], flag);
>>
>> flag has a constant value here.
>>
>
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