linux-kernel - Re: [PATCH] tty: serial: Replace deprecated PCI API

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Message-ID: <9f2960385d8ce318d3446fb6106f64b47781c730.camel@mailbox.org>
Date: Thu, 18 Dec 2025 10:30:18 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: phasta@...nel.org, Guenter Roeck <linux@...ck-us.net>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>,  linux-kernel@...r.kernel.org,
 linux-serial@...r.kernel.org, Florian Eckert <fe@....tdt.de>
Subject: Re: [PATCH] tty: serial: Replace deprecated PCI API

On Thu, 2025-12-18 at 10:02 +0100, Philipp Stanner wrote:
> +Cc Florian
> 
> On Wed, 2025-12-17 at 08:11 -0800, Guenter Roeck wrote:
> > On 12/17/25 06:06, Greg Kroah-Hartman wrote:
> > > On Thu, Dec 11, 2025 at 02:57:46PM +0100, Philipp Stanner wrote:
> > > > On Wed, 2025-11-26 at 09:02 -0800, Guenter Roeck wrote:
> > > > > On 11/26/25 01:10, Philipp Stanner wrote:
> > > > > > pcim_iomap_table() is deprecated. Moreover, its special usage in 8250,
> > > > > > causes a WARN_ON to fire (in pcim_add_mapping_to_legacy_table()).
> > > > > > 
> > > > > > 8250's function serial8250_pci_setup_port() effectively maps the same
> > > > > > BAR multiple times and adds an offset to the start address. While
> > > > > > mapping and adding offsets is not a bug, it can be achieved in a far
> > > > > > more straightforward way by using the specialized function
> > > > > > pcim_iomap_range().
> > > > > > 
> > > > > > pcim_iomap_range() does not add the mapping addresses to the deprecated
> > > > > > iomap table - that's not a problem, however, because non of the users of
> > > > > > serial8250_pci_setup_port() uses pcim_iomap_table().
> > > > > > 
> > > > > > Replace the deprecated PCI functions with pcim_iomap_range().
> > > > > > 
> > > > > > Cc: Guenter Roeck <linux@...ck-us.net>
> > > > > > Link: https://lore.kernel.org/dri-devel/16cd212f-6ea0-471d-bf32-34f55d7292fe@roeck-us.net/
> > > > > > Signed-off-by: Philipp Stanner <phasta@...nel.org>
> > > > > > ---
> > > > > > @Guenther: Can you please test this? I hope it fixes your issue.
> > > > > 
> > > > > Yes, it does. Thanks a lot for fixing this!
> > > > > 
> > > > > Tested-by: Guenter Roeck <linux@...ck-us.net>
> > > > 
> > > > @Greg:
> > > > Can you apply this?
> > > 
> > > Does not apply at all to 6.19-rc1 :(
> > > 
> > 
> > It conflicts with commit b7cefdb663382 ("serial: 8250_pcilib: Replace deprecated
> > PCI functions"). Unfortunately that commit does not fix the problem; I still
> > see it with v6.19-rc1.
> 
> Without me being too familiar with the code, it seems that that commit
> didn't do what it promised, which is getting rid of the multiple
> mappings of the same BAR. Presumably it is mapped multiple times
> through setup_port():
> 
> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
> index 152f914c599d..f0f13fdda2df 100644
> --- a/drivers/tty/serial/8250/8250_pci.c
> +++ b/drivers/tty/serial/8250/8250_pci.c
> @@ -165,7 +165,15 @@ static int
>  setup_port(struct serial_private *priv, struct uart_8250_port *port,
>            u8 bar, unsigned int offset, int regshift)
>  {
> -       return serial8250_pci_setup_port(priv->dev, port, bar, offset, regshift);
> +       void __iomem *iomem = NULL;
> +
> +       if (pci_resource_flags(priv->dev, bar) & IORESOURCE_MEM) {
> +               iomem = pcim_iomap(priv->dev, bar, 0);
> +               if (!iomem)
> +                       return -ENOMEM;
> +       }
> +
> +       return serial8250_pci_setup_port(priv->dev, port, bar, offset, regshift, iomem);
>  }
> 
> 
> Note that pcim_iomap() is the party that is *adding* the mappings to
> the legacy table, whereas pcim_iomap_table() was just used to access
> those.
> 
> In any case, I'm quite confident that this description of intended
> behavior from the commit message
> 
> "the remapping should only be called once via 'pcim_iomap()'. Therefore
> the remapping moved to the caller of 'serial8250_pci_setup_port()'."
> 
> has not been implemented in the actual code. Otherwise the WARN_ON
> couldn't fire.
> 
> 
> My personal opinion is that mapping the same BAR multiple times is not
> a bug and there is no real practical reason why it shouldn't be done
> when it can make sense. pci_iomap_range() exists for that reason since
> quite some time.
> 
> So my suggested fix for this would be to revert b7cefdb663382 and apply
> my patch here instead.


Ah, nevermind. I thought about it and it's probably safe to say that
that WARN_ON is useless anyways. So since Florian has already done the
work of getting rid of the deprecated function, I think the clean thing
to do is to remove the WARN_ON from PCI.

I proposed this to Bjorn today:
https://lore.kernel.org/all/20251218092819.149665-2-phasta@kernel.org/

Sorry for the noise

P.