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

Greg Kroah-Hartman
2025-07-29T08:48:20Z

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