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

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Message-ID: <92c2c05a-be0d-4017-a766-62832668512d@roeck-us.net>
Date: Fri, 22 Nov 2024 09:07:33 -0800
From: Guenter Roeck <linux@...ck-us.net>
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 11/22/24 07:35, Niklas Schnelle wrote:
> On Fri, 2024-11-22 at 07:18 -0800, Guenter Roeck wrote:
>> On Fri, Apr 05, 2024 at 05:29:24PM +0200, Niklas Schnelle wrote:
>>> In a future patch HAS_IOPORT=n will disable inb()/outb() and friends at
>>> compile time. We thus need to add HAS_IOPORT as dependency for those
>>> drivers using them unconditionally. For 8250 based drivers some support
>>> MMIO only use so fence only the parts requiring I/O ports.
>>>
>>> Co-developed-by: Arnd Bergmann <arnd@...nel.org>
>>> Signed-off-by: Arnd Bergmann <arnd@...nel.org>
>>> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
>> ...
>>> @@ -422,10 +443,12 @@ static void set_io_from_upio(struct uart_port *p)
>>>   	up->dl_write = default_serial_dl_write;
>>>   
>>> +	default:
>>> +		WARN(1, "Unsupported UART type %x\n", p->iotype);
>>
>> So, according to this patch, the serial uart on microblaze, nios2,
>> openrisc, xtensa, and possibly others is not or no longer supported.
>>
>> WARNING: CPU: 0 PID: 0 at drivers/tty/serial/8250/8250_port.c:470 serial8250_set_defaults+0x1a8/0x22c
>> Unsupported UART type 0
>>
>> Any special reason ?
>>
>> Guenter
> 
> So according to the warning the p->iotype is 0 which is UPIO_PORT.
> For UPIO_PORT the switch above the WARN would pick io_serial_in() and
> io_serial_out() as handlers. These use inb() respectively outb() to
> access the serial so I don't see how they would work with !HAS_IOPORT
> and it most definitely won't work for s390.
> 
> Now for Microblaze Kconfig says to select HAS_IOPORT if PCI so I'd
> assume that it can use inb()/outb() and maybe the PCI requirement is
> not correct if this isn't a PCI device and it used to work with
> inb()/outb()? For nios2, openrisc, and xtensa they don't select
> HAS_IOPORT so either it really won't work anyway or they should select
> it. Can you tell us more about the devices involved where you saw this?
> 

This is seen when booting the affected architectures with qemu.

Logs:

https://kerneltests.org/builders/qemu-microblaze-master/builds/327/steps/qemubuildcommand/logs/stdio
https://kerneltests.org/builders/qemu-nios2-master/builds/314/steps/qemubuildcommand/logs/stdio
https://kerneltests.org/builders/qemu-openrisc-master/builds/301
https://kerneltests.org/builders/qemu-xtensa-master/builds/311/steps/qemubuildcommand/logs/stdio

Guenter