linux-kernel - Re: [PATCH] PCI/sysfs: add write attribute for boot

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Date:   Sun, 26 Sep 2021 15:20:27 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Zhenneng Li <lizhenneng@...inos.cn>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/sysfs: add write attribute for boot_vga

On Sun, Sep 26, 2021 at 03:15:39PM +0800, Zhenneng Li wrote:
> Add writing attribute for boot_vga sys node,
> so we can config default video display
> output dynamically when there are two video
> cards on a machine.
> 
> Xorg server will determine running on which
> video card based on boot_vga node's value.

When you repost this, please take a look at the git commit log history
and make yours similar.  Specifically, the subject should start with a
capital letter, and the body should be rewrapped to fill 75
characters.

Please contrast this with the existing VGA arbiter.  See
Documentation/gpu/vgaarbiter.rst.  It sounds like this may overlap
with the VGA arbiter functionality, so this should explain why we need
both and how they interact.

> Signed-off-by: Zhenneng Li <lizhenneng@...inos.cn>
> ---
>  drivers/pci/pci-sysfs.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 7bbf2673c7f2..a6ba19ce7adb 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -664,7 +664,29 @@ static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr,
>  			  !!(pdev->resource[PCI_ROM_RESOURCE].flags &
>  			     IORESOURCE_ROM_SHADOW));
>  }
> -static DEVICE_ATTR_RO(boot_vga);
> +
> +static ssize_t boot_vga_store(struct device *dev, struct device_attribute *attr,
> +			      const char *buf, size_t count)
> +{
> +	unsigned long val;
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	struct pci_dev *vga_dev = vga_default_device();
> +
> +	if (kstrtoul(buf, 0, &val) < 0)
> +		return -EINVAL;
> +
> +	if (val != 1)
> +		return -EINVAL;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	if (pdev != vga_dev)
> +		vga_set_default_device(pdev);
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(boot_vga);
>  
>  static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
>  			       struct bin_attribute *bin_attr, char *buf,
> -- 
> 2.25.1
> 
> 
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