linux-kernel - Re: [PATCH] PCI: Remove useless WARN

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Message-ID: <20260114170059.GA822278@bhelgaas>
Date: Wed, 14 Jan 2026 11:00:59 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Philipp Stanner <phasta@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH] PCI: Remove useless WARN_ON() from devres

On Thu, Dec 18, 2025 at 10:28:20AM +0100, Philipp Stanner wrote:
> PCI's devres implementation contains a WARN_ON() which served to inform
> users relying on the legacy devres iomap table that this table does not
> support multiple mappings per BAR.
> 
> The WARN_ON() can be regarded as useless by now, since mapping a BAR
> multiple times is legal behavior and old users of pcim_iomap_table(),
> the accessor function for that table, did not break in the past PCI
> devres cleanup. New PCI users will hopefully notice that
> pcim_iomap_table() is deprecated and are unlikely to use it for mapping
> the same BAR multiple times.
> 
> Moreover, WARN_ON()s create noisy, difficult to read error messages
> which can be more confusing than helpful, since they don't inform the
> user about what precisely the problem is.
> 
> Remove the WARN_ON().
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Philipp Stanner <phasta@...nel.org>

Applied to pci/misc for v6.20, thanks!

> ---
>  drivers/pci/devres.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c
> index 9f4190501395..f075e7881c3a 100644
> --- a/drivers/pci/devres.c
> +++ b/drivers/pci/devres.c
> @@ -469,9 +469,6 @@ static int pcim_add_mapping_to_legacy_table(struct pci_dev *pdev,
>  	if (!legacy_iomap_table)
>  		return -ENOMEM;
>  
> -	/* The legacy mechanism doesn't allow for duplicate mappings. */
> -	WARN_ON(legacy_iomap_table[bar]);
> -
>  	legacy_iomap_table[bar] = mapping;
>  
>  	return 0;
> -- 
> 2.49.0
>