Re: [PATCH] tty: serial: 8250: exar: fix kernel warning in default_setup function

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jul 29, 2025 at 08:17:04AM +0000, Wilken Gottwalt wrote:
> Fixes:

But no "Fixes:" tag in the commit?  No cc: stable added?

> 
> [    2.601213] WARNING: CPU: 3 PID: 1 at pcim_iomap.part.0+0xbc/0xc0
> [    2.601224] Modules linked in:
> [    2.601230] CPU: 3 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.38-vanilla-standard #1
> [    2.601237] Hardware name: Default string Default string/CXC-BT-JERO, BIOS S1.61.1.0# 09/17/2018
> [    2.601241] RIP: 0010:pcim_iomap.part.0+0xbc/0xc0
> [    2.601248] Code: 31 ed e8 07 a5 14 00 4c 89 e8 5b 41 5c 41 5d 41 5e 5d c3 cc cc cc cc 45 31 ed 5b 41 5c 4c 89 e8 41 5d 41 5e 5d c3 cc cc cc cc <0f> 0b eb a0 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f
> [    2.601253] RSP: 0000:ffffa7444001f830 EFLAGS: 00010286
> [    2.601259] RAX: ffffa066c1321f28 RBX: 0000000000000000 RCX: ffffa066c1215330
> [    2.601264] RDX: 0000000000000001 RSI: 0000000000000286 RDI: ffffa066c121532c
> [    2.601268] RBP: ffffa7444001f850 R08: 0000000000000000 R09: 0000000000000286
> [    2.601272] R10: 0000000000000000 R11: 000ffffffffff000 R12: ffffa066c1215000
> [    2.601275] R13: ffffa744403b0000 R14: ffffa066c1310208 R15: ffffa066c12150c8
> [    2.601279] FS:  0000000000000000(0000) GS:ffffa067d7d80000(0000) knlGS:0000000000000000
> [    2.601284] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    2.601288] CR2: 0000000000000000 CR3: 000000005f22a000 CR4: 00000000001006f0
> [    2.601292] Call Trace:
> [    2.601296]  <TASK>
> [    2.601301]  pcim_iomap+0x1a/0x20
> [    2.601308]  serial8250_pci_setup_port+0xea/0x190
> [    2.601337]  default_setup.constprop.0+0x27/0x90
> [    2.601347]  pci_xr17v35x_setup+0xd0/0x190
> [    2.601355]  exar_pci_probe+0x297/0x400
> [    2.601365]  ? __pfx_generic_rs485_config+0x10/0x10
> [    2.601383]  local_pci_probe+0x4b/0xb0
> [    2.601390]  pci_device_probe+0xc5/0x200
> [    2.601397]  really_probe+0xe5/0x390
> [    2.601405]  __driver_probe_device+0x7e/0x160
> [    2.601412]  driver_probe_device+0x23/0xa0
> [    2.601418]  __driver_attach+0xe4/0x1e0
> [    2.601424]  ? __pfx___driver_attach+0x10/0x10
> [    2.601431]  bus_for_each_dev+0x7d/0xd0
> [    2.601438]  driver_attach+0x1e/0x30
> [    2.601444]  bus_add_driver+0x114/0x240
> [    2.601450]  driver_register+0x64/0x130
> [    2.601457]  ? __pfx_exar_pci_driver_init+0x10/0x10
> [    2.601466]  __pci_register_driver+0x61/0x70
> [    2.601471]  exar_pci_driver_init+0x1e/0x30
> [    2.601479]  do_one_initcall+0x49/0x310
> [    2.601487]  kernel_init_freeable+0x1aa/0x2e0
> [    2.601495]  ? __pfx_kernel_init+0x10/0x10
> [    2.601503]  kernel_init+0x1a/0x1c0
> [    2.601510]  ret_from_fork+0x3c/0x60
> [    2.601516]  ? __pfx_kernel_init+0x10/0x10
> [    2.601523]  ret_from_fork_asm+0x1a/0x30
> [    2.601531]  </TASK>
> 
> >From kernel 6.8 to 6.9 the default_setup function was changed to use the
> more generic serial8250_pci_setup_port function to setup the serial
> ports, but that results in this kernel warning.
> 
> The serial8250_pci_setup_port function internally relies on the
> pcim_iomap function. The way this function works was changed from kernel
> 6.10 to 6.11 and now clearly states in the description "This SHOULD only
> be used once per BAR". And this is the issue. Basically all the hardware
> handled by the 8250_exar driver are multi-port cards, which have
> multiple ports on one PCI bar. The serial8250_pci_setup_port/pcim_iomap
> functions can not be used with that driver anymore. Reverting the code
> back to the older pci_resource_start approach fixes this issue.

These two paragraphs should be above the warning splat.


> 
> Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
> ---
>  drivers/tty/serial/8250/8250_exar.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
> index 04a0cbab02c2..5660bb897803 100644
> --- a/drivers/tty/serial/8250/8250_exar.c
> +++ b/drivers/tty/serial/8250/8250_exar.c
> @@ -500,12 +500,13 @@ static int default_setup(struct exar8250 *priv, struct pci_dev *pcidev,
>  			 struct uart_8250_port *port)
>  {
>  	const struct exar8250_board *board = priv->board;
> +	unsigned int bar = 0;

Why is this needed?

>  	unsigned char status;
> -	int err;
>  
> -	err = serial8250_pci_setup_port(pcidev, port, 0, offset, board->reg_shift);
> -	if (err)
> -		return err;
> +	port->port.iotype = UPIO_MEM;
> +	port->port.mapbase = pci_resource_start(pcidev, bar) + offset;
> +	port->port.membase = priv->virt + offset;
> +	port->port.regshift = board->reg_shift;

And so now serial8250_pci_setup_port() is never called?  Are you sure
that's ok?

thanks,

greg k-h