On Fri, Dec 27, 2024 at 11:51:21PM +0106, John Ogness wrote:
> Implement the necessary callbacks to switch the 8250 console driver
> to perform as an nbcon console.
>
> Add implementations for the nbcon console callbacks:
>
> ->write_atomic()
> ->write_thread()
> ->device_lock()
> ->device_unlock()
>
> and add CON_NBCON to the initial @flags.
>
> All register access in the callbacks are within unsafe sections.
> The ->write_atomic and ->write_therad() callbacks allow safe
->write_atomic()
> handover/takeover per byte and add a preceding newline if they
> take over from another context mid-line.
>
> For the ->write_atomic() callback, a new irq_work is used to defer
> modem control since it may be called from a context that does not
> allow waking up tasks.
>
> Note: A new __serial8250_clear_IER() is introduced for direct
> clearing of UART_IER. This will allow to restore the lockdep
> check to serial8250_clear_IER() in a follow-up commit.
...
> if (toggle_ier) {
> + /*
> + * Port locked to synchronize UART_IER access
> + * against the console
Missing period in multi-line comment.
> + */
> + lockdep_assert_held_once(&p->port.lock);
> +
> p->ier |= UART_IER_RLSI | UART_IER_RDI;
> serial_port_out(&p->port, UART_IER, p->ier);
> }
...
> -static void fifo_wait_for_lsr(struct uart_8250_port *up, unsigned int count)
> +static int fifo_wait_for_lsr(struct uart_8250_port *up,
> + struct nbcon_write_context *wctxt,
> + unsigned int count)
> {
> unsigned int i;
>
> for (i = 0; i < count; i++) {
> + if (!nbcon_can_proceed(wctxt))
> + return -EPERM;
> +
> if (wait_for_lsr(up, UART_LSR_THRE))
> - return;
> + return 0;
> }
> +
> + return -ETIMEDOUT;
> }
...
> static void serial8250_console_fifo_write(struct uart_8250_port *up,
> - const char *s, unsigned int count)
> + struct nbcon_write_context *wctxt)
> {
> - const char *end = s + count;
> unsigned int fifosize = up->tx_loadsz;
> struct uart_port *port = &up->port;
> + const char *s = wctxt->outbuf;
> + const char *end = s + wctxt->len;
> unsigned int tx_count = 0;
> bool cr_sent = false;
> unsigned int i;
>
> while (s != end) {
> /* Allow timeout for each byte of a possibly full FIFO */
> - fifo_wait_for_lsr(up, fifosize);
> + if (fifo_wait_for_lsr(up, wctxt, fifosize) == -EPERM)
> + return;
Perhaps it was already discussed and I forgot about it or hadn't read,
but I don't get how per-byte check for NBCON permission can help if there
is something already in the HW FIFO?
I mean in _this_ case wouldn't be enough to check FIFO to drain and only after
that check the permission?
> for (i = 0; i < fifosize && s != end; ++i) {
> if (*s == '\n' && !cr_sent) {
> * Allow timeout for each byte written since the caller will only wait
> * for UART_LSR_BOTH_EMPTY using the timeout of a single character
> */
> - fifo_wait_for_lsr(up, tx_count);
> + fifo_wait_for_lsr(up, wctxt, tx_count);
> +}
...
> + if (up->msr_saved_flags) {
> + /*
> + * For atomic, it must be deferred to irq_work because this
> + * may be a context that does not permit waking up tasks.
> + */
> + if (is_atomic)
> + irq_work_queue(&up->modem_status_work);
> + else
> + serial8250_modem_status(up);
Hmm... Shouldn't this be part of _modem_status() for all drivers using this call?
> + }
...
> + bool console_line_ended; /* line fully output */
Sorry, I didn't get the comment. Do you meant "line is fully printed out
[to HW]"?
--
With Best Regards,
Andy Shevchenko
