linux-kernel - Re: [PATCH 1/1] tty: serial: handle HAS

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Date: Thu, 23 May 2024 03:11:16 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, 
    Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
    linux-serial@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>, 
    Heiko Carstens <hca@...ux.ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] tty: serial: handle HAS_IOPORT dependencies

On Fri, 5 Apr 2024, Niklas Schnelle wrote:

> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
> index 0d35c77fad9e..38ac5236d2ea 100644
> --- a/drivers/tty/serial/8250/8250_pci.c
> +++ b/drivers/tty/serial/8250/8250_pci.c
> @@ -928,6 +928,7 @@ static int pci_netmos_init(struct pci_dev *dev)
>  	return num_serial;
>  }
>  
> +#ifdef CONFIG_HAS_IOPORT
>  /*
>   * These chips are available with optionally one parallel port and up to
>   * two serial ports. Unfortunately they all have the same product id.
[...]
> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> index 47ff50763c04..54bf98869abf 100644
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -136,7 +135,7 @@ config SERIAL_8250_PCILIB
>  
>  config SERIAL_8250_PCI
>  	tristate "8250/16550 PCI device support"
> -	depends on SERIAL_8250 && PCI
> +	depends on SERIAL_8250 && PCI && HAS_IOPORT
>  	select SERIAL_8250_PCILIB
>  	default SERIAL_8250
>  	help

 This is clearly wrong, there is PCIe 8250 serial hardware that does MMIO 
only, so the option has to stay possible to enable.  I have such hardware 
as shown in this log:

Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
serial 0001:01:00.0: enabling device (0140 -> 0142)
serial 0001:01:00.0: detected caps 00000700 should be 00000500
0001:01:00.0: ttyS0 at MMIO 0x600c080401000 (irq = 40, base_baud = 15625000) is a 16C950/954
serial 0001:01:00.0: detected caps 00000700 should be 00000500
0001:01:00.0: ttyS1 at MMIO 0x600c080401200 (irq = 40, base_baud = 15625000) is a 16C950/954

which is from a POWER9 system.  Which as you may know has no PCI port I/O 
support in hardware, so it is quite relevant here.  I'd like to keep this 
PCIe serial option functional with my system.

 Also your change itself modifies 8250_pci.c (cited above for reference), 
which would make no sense if SERIAL_8250_PCI was permanently disabled for 
!HAS_IOPORT.  Shall I take it than that the Kconfig change I question has 
been made merely by mistake?

  Maciej