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

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Message-ID: <8fe35d82-bee7-03e1-6e07-73df9f351728@linux.intel.com>
Date: Thu, 12 Jun 2025 12:18:39 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Jiri Slaby <jirislaby@...nel.org>
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 Thu, 12 Jun 2025, Jiri Slaby wrote:

> 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;
> > }
> > 
> 
> ?

I don't know what part exactly you wanted to ask about but it looks mostly 
fine (sans what is broken due to email).

-- 
 i.