Re: [PATCH 2/3] PCI: vmd: Expose VMD details from BIOS

[Andrew Murray <andrew.murray@arm.com>]

On Fri, Nov 01, 2019 at 02:24:02PM +0000, Derrick, Jonathan wrote:
> Hi ANdrew,
> 
> Thanks for the review
> 
> On Fri, 2019-11-01 at 13:16 +0000, Andrew Murray wrote:
> > On Wed, Oct 16, 2019 at 11:04:47AM -0600, Jon Derrick wrote:
> > > When some VMDs are enabled and others are not, it's difficult to
> > > determine which IIO stack corresponds to the enabled VMD.
> > > 
> > > To assist userspace with management tasks, VMD BIOS will write the VMD
> > > instance number and socket number into the first enabled root port's IO
> > > Base/Limit registers prior to OS handoff. VMD driver can capture this
> > > information and expose it to userspace.
> > > 
> > > Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > ---
> > >  drivers/pci/controller/vmd.c | 79 ++++++++++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 77 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > > index 959c7c7..dbe1bff 100644
> > > --- a/drivers/pci/controller/vmd.c
> > > +++ b/drivers/pci/controller/vmd.c
> > > @@ -98,6 +98,8 @@ struct vmd_dev {
> > >  	struct irq_domain	*irq_domain;
> > >  	struct pci_bus		*bus;
> > >  	u8			busn_start;
> > > +	u8			socket_nr;
> > > +	u8			instance_nr;
> > >  
> > >  	struct dma_map_ops	dma_ops;
> > >  	struct dma_domain	dma_domain;
> > > @@ -543,6 +545,74 @@ static int vmd_pci_write(struct pci_bus *bus, unsigned int devfn, int reg,
> > >  	.write		= vmd_pci_write,
> > >  };
> > >  
> > > +/**
> > > + * for_each_vmd_root_port - iterate over all enabled VMD Root Ports
> > > + * @vmd: &struct vmd_dev VMD device descriptor
> > > + * @rp: int iterator cursor
> > > + * @temp: u32 temporary value for config read
> > > + *
> > > + * VMD Root Ports are located in the VMD PCIe Domain at 00:[0-3].0, and config
> > > + * space can be determinately accessed through the VMD Config BAR. Because VMD
> > > + * Root Ports can be individually disabled, it's important to iterate for the
> > > + * first enabled Root Port as determined by reading the Vendor/Device register.
> > > + */
> > > +#define for_each_vmd_root_port(vmd, rp, temp)				\
> > > +	for (rp = 0; rp < 4; rp++)					\
> > > +		if (vmd_cfg_read(vmd, 0, PCI_DEVFN(root_port, 0),	\
> > > +				 PCI_VENDOR_ID, 4, &temp) ||		\
> > > +		    temp == 0xffffffff) {} else
> > 
> > You may want to consider using PCI_ERROR_RESPONSE here instead of 0xffffffff.
> > Though this hasn't yet been merged:
> > 
> > https://patchwork.ozlabs.org/project/linux-pci/list/?series=126820
> > 
> 
> Sure it will fit this case perfectly once it's merged
> 
> > > +
> > > +static int vmd_parse_domain(struct vmd_dev *vmd)
> > > +{
> > > +	int root_port, ret;
> > > +	u32 temp, iobase;
> > > +
> > > +	vmd->socket_nr = -1;
> > > +	vmd->instance_nr = -1;
> > > +
> > > +	for_each_vmd_root_port(vmd, root_port, temp) {
> > > +		ret = vmd_cfg_read(vmd, 0, PCI_DEVFN(root_port, 0),
> > > +				   PCI_IO_BASE, 2, &iobase);
> > > +		if (ret)
> > > +			return ret;
> > > +
> > > +		vmd->socket_nr = (iobase >> 4) & 0xf;
> > > +		vmd->instance_nr = (iobase >> 14) & 0x3;
> > 
> > I'm not familiar with VMD - however how can you be sure that the VMD BIOS
> > will always populate these values here? Is it possible that earlier BIOS's
> > won't do this and something will go wrong here?
> > 
> > Is there any sanity checking that can happen here?
> 
> Yes that's entirely possible and would show indeterminate values in
> that case. It would be up to the user to understand if the BIOS
> supports the mode before relying on the data.
> 
> I am investigating to see if we can do a dmi_match to verify the data
> before publishing.

I think that would be helpful if possible as it would simplify the
user software - and also prevent the user ever getting garbage data.

> 
> 
> > 
> > > +
> > > +		/* First available will be used */
> > > +		break;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static ssize_t socket_nr_show(struct device *dev,
> > > +			      struct device_attribute *attr, char *buf)
> > > +{
> > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > > +	struct vmd_dev *vmd = pci_get_drvdata(pdev);
> > > +
> > > +	return sprintf(buf, "%u\n", vmd->socket_nr);
> > > +}
> > > +static DEVICE_ATTR_RO(socket_nr);
> > > +
> > > +static ssize_t instance_nr_show(struct device *dev,
> > > +			      struct device_attribute *attr, char *buf)
> > > +{
> > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > > +	struct vmd_dev *vmd = pci_get_drvdata(pdev);
> > > +
> > > +	return sprintf(buf, "%u\n", vmd->instance_nr);
> > > +}
> > > +static DEVICE_ATTR_RO(instance_nr);
> > > +
> > > +static struct attribute *vmd_dev_attrs[] = {
> > > +	&dev_attr_socket_nr.attr,
> > > +	&dev_attr_instance_nr.attr,
> > > +	NULL
> > > +};
> > > +ATTRIBUTE_GROUPS(vmd_dev);
> > > +
> > >  static void vmd_attach_resources(struct vmd_dev *vmd)
> > >  {
> > >  	vmd->dev->resource[VMD_MEMBAR1].child = &vmd->resources[1];
> > > @@ -582,6 +652,11 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
> > >  	resource_size_t offset[2] = {0};
> > >  	resource_size_t membar2_offset = 0x2000;
> > >  	struct pci_bus *child;
> > > +	int ret;
> > > +
> > > +	ret = vmd_parse_domain(vmd);
> > > +	if (ret)
> > > +		return ret;
> > 
> > This always will succeed. But what happens if this function returns yet
> > socket_nr/instance_nr hasn't been written to? Is that OK?
> > 
> 
> Basically only one possibility that could occur and that's if the VMD
> is enabled without any VMD Root Ports being enabled on the VMD domain.
> It's an odd configuration but is technically valid, although the domain
> becomes useless until the user reboots and enables the VMD Root Ports. 
> 
> So it's more-or-less implied either socket_nr/instance_nr will have
> data or the domain won't be usable.

Of course in this case, the default value will be -1, which should be
quite obvious to a user that this isn't a valid value.

Thanks,

Andrew Murray

> 
> Thanks,
> Jon
> 
> 
> > Thanks,
> > 
> > Andrew Murray
> > 
> > >  
> > >  	/*
> > >  	 * Shadow registers may exist in certain VMD device ids which allow
> > > @@ -591,7 +666,6 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
> > >  	 */
> > >  	if (features & VMD_FEAT_HAS_MEMBAR_SHADOW) {
> > >  		u32 vmlock;
> > > -		int ret;
> > >  
> > >  		membar2_offset = MB2_SHADOW_OFFSET + MB2_SHADOW_SIZE;
> > >  		ret = pci_read_config_dword(vmd->dev, PCI_REG_VMLOCK, &vmlock);
> > > @@ -876,7 +950,8 @@ static int vmd_resume(struct device *dev)
> > >  	.probe		= vmd_probe,
> > >  	.remove		= vmd_remove,
> > >  	.driver		= {
> > > -		.pm	= &vmd_dev_pm_ops,
> > > +		.pm		= &vmd_dev_pm_ops,
> > > +		.dev_groups	= vmd_dev_groups,
> > >  	},
> > >  };
> > >  module_pci_driver(vmd_drv);
> > > -- 
> > > 1.8.3.1
> > >