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

Wilken Gottwalt
2025-07-29T09:32:27Z

On Tue, 29 Jul 2025 10:48:17 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> 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?

It is a long time I ago I did a fixes patch, argh. Hmm, it was a line like this
Fixes: 123456789012 ("bla: bla: aaaahhh"), right? I will fix that. Though, I'm
not sure if I should refer the pcim_iomap change here, or the change in the exar
drivers default_setup. The point is, the first change, the default_setup one was
fine until the later pcim_iomap change was done. The later change basically
affects hundrets of drivers, while the default_setup change is limited to the
8250 exar driver only. I will not touch pcim_iomap. What do you think about
this?

> >
> > [ 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.

Yeah, I wasn't sure about this. Will fix this.

> >
> > 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?

It was the original code, I just reverted it. The idea was to go back to code,
which was there for several kernel generations and worked flawlessly. But yes,
that can be optimized. I can change this.

> > 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?

Not by this exar driver, but other serial port drivers (8250_pci1xxxx, 8250_pci)
use it, just like it was before the change in kernel 6.9.

> thanks,
>
> greg k-h

Thanks for the feedback.

greetings,
Wilken