linux-kernel - Re: PCI: Disable not requested resource types in pci_enable

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Message-ID: <20200710210924.GA80868@bjorn-Precision-5520>
Date:   Fri, 10 Jul 2020 16:09:24 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PCI: Disable not requested resource types in pci_enable_resources

On Thu, May 28, 2020 at 08:47:12PM +0200, Heiner Kallweit wrote:
> Currently, if both resource types are enabled before the call, the mask
> value doesn't matter. Means as of today I wouldn't be able to e.g.
> disable PCI_COMMAND_IO. At least my interpretation is that mask defines
> which resource types are enabled after the call. Therefore change the
> behavior to disable not requested resource types.
> 
> At least on my x86 devices this change doesn't have side effects.

Does this have a practical benefit?  If it fixes a bug or if there's
something useful we can do because of this patch, I'll push it higher
up the priority list.

> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/pci/setup-res.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> index d21fa04fa..6ef458c10 100644
> --- a/drivers/pci/setup-res.c
> +++ b/drivers/pci/setup-res.c
> @@ -459,8 +459,8 @@ int pci_enable_resources(struct pci_dev *dev, int mask)
>  	int i;
>  	struct resource *r;
>  
> -	pci_read_config_word(dev, PCI_COMMAND, &cmd);
> -	old_cmd = cmd;
> +	pci_read_config_word(dev, PCI_COMMAND, &old_cmd);
> +	cmd = old_cmd & ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
>  
>  	for (i = 0; i < PCI_NUM_RESOURCES; i++) {
>  		if (!(mask & (1 << i)))
> -- 
> 2.26.2
>