On Fri, Oct 25, 2024 at 01:03:27PM +0206, 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.
Again, use consistent style for the references to the callbacks.
it may be .func, or ->func(), or something else, but make it consistent.
> All register access in the callbacks are within unsafe sections.
> The write callbacks allow safe handover/takeover per byte and add
> a preceding newline if they take over mid-line.
>
> For the write_atomic() case, a new irq_work is used to defer modem
> control since it may be a context that does not allow waking up
> tasks.
...
> +/*
> + * Only to be used directly by the console write callbacks, which may not
> + * require the port lock. Use serial8250_clear_IER() instead for all other
> + * cases.
> + */
> +static void __serial8250_clear_IER(struct uart_8250_port *up)
> {
> if (up->capabilities & UART_CAP_UUE)
> serial_out(up, UART_IER, UART_IER_UUE);
> serial_out(up, UART_IER, 0);
> }
>
> +static inline void serial8250_clear_IER(struct uart_8250_port *up)
> +{
> + __serial8250_clear_IER(up);
Shouldn't this have a lockdep annotation to differentiate with the above?
> +}
...
> +static void serial8250_console_byte_write(struct uart_8250_port *up,
> + struct nbcon_write_context *wctxt)
> +{
> + const char *s = READ_ONCE(wctxt->outbuf);
> + const char *end = s + READ_ONCE(wctxt->len);
Is there any possibility that outbuf value be changed before we get the len and
at the end we get the wrong pointer?
> + struct uart_port *port = &up->port;
> +
> + /*
> + * Write out the message. Toggle unsafe for each byte in order to give
> + * another (higher priority) context the opportunity for a friendly
> + * takeover. If such a takeover occurs, this must abort writing since
> + * wctxt->outbuf and wctxt->len are no longer valid.
> + */
> + while (s != end) {
> + if (!nbcon_enter_unsafe(wctxt))
> + return;
> +
> + uart_console_write(port, s++, 1, serial8250_console_wait_putchar);
> +
> + if (!nbcon_exit_unsafe(wctxt))
> + return;
> }
> }
...
> +/*
> + * irq_work handler to perform modem control. Only triggered via
> + * write_atomic() callback because it may be in a scheduler or NMI
Also make same style for the callback reference in the comments.
> + * context, unable to wake tasks.
> + */
...
> struct uart_8250_port {
> u16 lsr_save_mask;
> #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
> unsigned char msr_saved_flags;
> + struct irq_work modem_status_work;
> +
> + bool console_line_ended; /* line fully output */
>
> struct uart_8250_dma *dma;
> const struct uart_8250_ops *ops;
Btw, have you run `pahole` on this? Perhaps there are better places for new
members?
--
With Best Regards,
Andy Shevchenko
