Re: [PATCH] PCI/sysfs: add write attribute for boot_vga

[李真能]

在 2021/9/27 上午4:20, Bjorn Helgaas 写道:
> 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.

"Some "legacy" VGA devices implemented on PCI typically have the same 
hard-decoded addresses as they did on ISA. When multiple PCI devices are 
accessed at same time they need some kind of coordination. ", this is 
the explain of config VGA_ARB, that is to say, some legacy vga devices 
need use the same pci bus address, if user app(such as xorg) want access 
card A, but card A and card B have same bus address,  then VGA 
agaarbiter will determine will card to be accessed.

And xorg will read boot_vga to determine which graphics card is the 
primary graphics output device.

That is the difference about boot_vga and vgaarbiter.



> > Signed-off-by: Zhenneng Li <lizhenneng@xxxxxxxxxx>
> > ---
> >   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
> >
> >
> > No virus found
> > 		Checked by Hillstone Network AntiVirus