Re: [PATCH v3 2/9] cxl/acpi: Extract component registers of restricted hosts from RCRB

From: Robert Richter
Date: Tue Nov 15 2022 - 07:18:54 EST


On 14.11.22 13:30:01, Dan Williams wrote:
> Robert Richter wrote:

> > diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
> > index ec178e69b18f..7a5bde81e949 100644
> > --- a/drivers/cxl/core/regs.c
> > +++ b/drivers/cxl/core/regs.c
> > @@ -307,3 +307,49 @@ int cxl_find_regblock(struct pci_dev *pdev, enum cxl_regloc_type type,
> > return -ENODEV;
> > }
> > EXPORT_SYMBOL_NS_GPL(cxl_find_regblock, CXL);
> > +
> > +resource_size_t cxl_rcrb_to_component(struct device *dev,
> > + resource_size_t rcrb,
> > + enum cxl_rcrb which)
> > +{
> > + resource_size_t component_reg_phys;
> > + u32 bar0, bar1;
> > + void *addr;
> > +
> > + if (which == CXL_RCRB_UPSTREAM)
> > + rcrb += SZ_4K;
> > +
> > + /*
> > + * RCRB's BAR[0..1] point to component block containing CXL
> > + * subsystem component registers. MEMBAR extraction follows
> > + * the PCI Base spec here, esp. 64 bit extraction and memory
> > + * ranges alignment (6.0, 7.5.1.2.1).
> > + */
>
> A request_mem_region() is needed here to ensure ownership and expected
> sequencing of accessing the RCRB to locate the component registers, and
> accessing the RCRB to manipulate the component registers. It also helps
> to sanity check that the BIOS mapped an exclusive range for the RCRB.

Right, that is missing.

>
> > + addr = ioremap(rcrb, PCI_BASE_ADDRESS_0 + SZ_8);
>
> That PCI_BASE_ADDRESS_0 does not belong there. It ends up being benign
> and forcing ioremap to map 12K instead of 8K, but it is a
> config-register offset, not part of the RCRB size.

Note this is BAR0 + 8 bytes, not 8k, and it does not map the whole
RCRB region but instead the first part of the config space up to
including the 64 bit BAR.

>
> > + if (!addr) {
> > + dev_err(dev, "Failed to map region %pr\n", addr);
> > + return CXL_RESOURCE_NONE;
> > + }
> > +
> > + bar0 = readl(addr + PCI_BASE_ADDRESS_0);
> > + bar1 = readl(addr + PCI_BASE_ADDRESS_1);
> > + iounmap(addr);
>
> ...corresponding release_mem_region() would go here.
>
> > +
> > + /* sanity check */
> > + if (bar0 & (PCI_BASE_ADDRESS_MEM_TYPE_1M | PCI_BASE_ADDRESS_SPACE_IO))
> > + return CXL_RESOURCE_NONE;
>
> I would have also expected:
>
> - a sanity check for "Memory Space Enable" being set in the command
> register.

Ok.

>
> - an explicit check for 0xffffffff for the case when the upstream-port
> implements "no RCRB" mode.

Yes, I left support for this to a later patch, but it's better to
check it here already and possibly fall back to reg loc DVSEC then.

>
> - some check that BIOS initialized the BAR values post reset given these
> BARs are invisible to the PCI core resource assignment

What check do you have in mind here? There is already the NULL check
which would be the out-of-reset value.

Thanks,

-Robert