linux-kernel - Re: [PATCH 15/33] serial: 8250: extract serial8250_THRE

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Message-ID: <b6c85f8e-da53-4268-ae34-421dcf9e373c@kernel.org>
Date: Thu, 12 Jun 2025 10:54:07 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-serial <linux-serial@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 15/33] serial: 8250: extract serial8250_THRE_test()

On 11. 06. 25, 14:03, Ilpo Järvinen wrote:
> On Wed, 11 Jun 2025, Jiri Slaby (SUSE) wrote:
...
>> +	/*
>> +	 * Test for UARTs that do not reassert THRE when the transmitter is idle and the interrupt
>> +	 * has already been cleared.  Real 16550s should always reassert this interrupt whenever the
>> +	 * transmitter is idle and the interrupt is enabled.  Delays are necessary to allow register
>> +	 * changes to become visible.
> 
> Very long comment lines are hard to read. (This is mostly not related to
> line length limits, but with eye movement required.)
> 
> It may make sense to place some of the descriptive comment text into a
> function comment instead of placing them mid-function.
> 
>> +	 *
>> +	 * Synchronize UART_IER access against the console.
>> +	 */
>> +	uart_port_lock_irqsave(port, &flags);
>> +
>> +	wait_for_xmitr(up, UART_LSR_THRE);
>> +	serial_port_out_sync(port, UART_IER, UART_IER_THRI);
>> +	udelay(1); /* allow THRE to set */
> 
> These comments mix visually into the code making this look a big wall of
> text overall. Maybe consider adding empty lines to the logic as well as
> there are what looks clear steps in this logic.


What about this:
> /*
>  * Test for UARTs that do not reassert THRE when the transmitter is idle and the
>  * interrupt has already been cleared. Real 16550s should always reassert this
>  * interrupt whenever the transmitter is idle and the interrupt is enabled.
>  * Delays are necessary to allow register changes to become visible.
>  */
> static void serial8250_THRE_test(struct uart_port *port)
> {       
>         struct uart_8250_port *up = up_to_u8250p(port);
>         unsigned long flags;
>         bool iir_noint1, iir_noint2;
> 
>         if (!port->irq)
>                 return;
>                         
>         if (up->port.flags & UPF_NO_THRE_TEST)
>                 return;
>         
>         if (port->irqflags & IRQF_SHARED)
>                 disable_irq_nosync(port->irq);
>         
>         /* Synchronize UART_IER access against the console. */
>         uart_port_lock_irqsave(port, &flags);
>         
>         wait_for_xmitr(up, UART_LSR_THRE);
>         serial_port_out_sync(port, UART_IER, UART_IER_THRI);
>         /* allow THRE to set */
>         udelay(1); 
> 
>         iir_noint1 = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
>         serial_port_out(port, UART_IER, 0);
>         serial_port_out_sync(port, UART_IER, UART_IER_THRI);
>         /* allow a working UART time to re-assert THRE */
>         udelay(1); 
> 
>         iir_noint2 = serial_port_in(port, UART_IIR) & UART_IIR_NO_INT;
>         serial_port_out(port, UART_IER, 0);
> 
>         uart_port_unlock_irqrestore(port, flags);
> 
>         if (port->irqflags & IRQF_SHARED)
>                 enable_irq(port->irq); 
>                         
>         /*
>          * If the interrupt is not reasserted, or we otherwise don't trust the
>          * iir, setup a timer to kick the UART on a regular basis.
>          */
>         if ((!iir_noint1 && iir_noint2) || up->port.flags & UPF_BUG_THRE)
>                 up->bugs |= UART_BUG_THRE;
> }
> 

?

thanks,
-- 
js
suse labs