Re: [RFC PATCH 4/9] cxl/mem: Map memory device registers

Ben Widawsky
2020-11-14T01:13:02Z

On 20-11-13 12:17:32, Bjorn Helgaas wrote:
> On Tue, Nov 10, 2020 at 09:43:51PM -0800, Ben Widawsky wrote:
> > All the necessary bits are initialized in order to find and map the
> > register space for CXL Memory Devices. This is accomplished by using the
> > Register Locator DVSEC (CXL 2.0 - 8.1.9.1) to determine which PCI BAR to
> > use, and how much of an offset from that BAR should be added.
>
> "Initialize the necessary bits ..." to use the usual imperative
> sentence structure, as you did in the subject.
>
> > If the memory device registers are found and mapped a new internal data
> > structure tracking device state is allocated.
>
> "Allocate device state if we find device registers" or similar.
>
> > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > ---
> > drivers/cxl/mem.c | 68 +++++++++++++++++++++++++++++++++++++++++++----
> > drivers/cxl/pci.h | 6 +++++
> > 2 files changed, 69 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index aa7d881fa47b..8d9b9ab6c5ea 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -7,9 +7,49 @@
> > #include "pci.h"
> >
> > struct cxl_mem {
> > + struct pci_dev *pdev;
> > void __iomem *regs;
> > };
> >
> > +static struct cxl_mem *cxl_mem_create(struct pci_dev *pdev, u32 reg_lo, u32 reg_hi)
> > +{
> > + struct device *dev = &pdev->dev;
> > + struct cxl_mem *cxlm;
> > + void __iomem *regs;
> > + u64 offset;
> > + u8 bar;
> > + int rc;
> > +
> > + offset = ((u64)reg_hi << 32) | (reg_lo & 0xffff0000);
> > + bar = reg_lo & 0x7;
> > +
> > + /* Basic sanity check that BAR is big enough */
> > + if (pci_resource_len(pdev, bar) < offset) {
> > + dev_err(dev, "bar%d: %pr: too small (offset: %#llx)\n",
> > + bar, &pdev->resource[bar], (unsigned long long) offset);
>
> s/bar/BAR/
>
> > + return ERR_PTR(-ENXIO);
> > + }
> > +
> > + rc = pcim_iomap_regions(pdev, 1 << bar, pci_name(pdev));
> > + if (rc != 0) {
> > + dev_err(dev, "failed to map registers\n");
> > + return ERR_PTR(-ENXIO);
> > + }
> > +
> > + cxlm = devm_kzalloc(&pdev->dev, sizeof(*cxlm), GFP_KERNEL);
> > + if (!cxlm) {
> > + dev_err(dev, "No memory available\n");
> > + return ERR_PTR(-ENOMEM);
> > + }
> > +
> > + regs = pcim_iomap_table(pdev)[bar];
> > + cxlm->pdev = pdev;
> > + cxlm->regs = regs + offset;
> > +
> > + dev_dbg(dev, "Mapped CXL Memory Device resource\n");
> > + return cxlm;
> > +}
> > +
> > static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
> > {
> > int pos;
> > @@ -34,9 +74,9 @@ static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
> >
> > static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > {
> > + struct cxl_mem *cxlm = ERR_PTR(-ENXIO);
> > struct device *dev = &pdev->dev;
> > - struct cxl_mem *cxlm;
>
> The order was better before ("dev", then "clxm"). Oh, I suppose this
> is a "reverse Christmas tree" thing.
>

I don't actually care either way as long as it's consistent. I tend to do
reverse Christmas tree for no particular reason.

> > - int rc, regloc;
> > + int rc, regloc, i;
> >
> > rc = cxl_bus_prepared(pdev);
> > if (rc != 0) {
> > @@ -44,15 +84,33 @@ static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > return rc;
> > }
> >
> > + rc = pcim_enable_device(pdev);
> > + if (rc)
> > + return rc;
> > +
> > regloc = cxl_mem_dvsec(pdev, PCI_DVSEC_ID_CXL_REGLOC);
> > if (!regloc) {
> > dev_err(dev, "register location dvsec not found\n");
> > return -ENXIO;
> > }
> > + regloc += 0xc; /* Skip DVSEC + reserved fields */
> > +
> > + for (i = regloc; i < regloc + 0x24; i += 8) {
> > + u32 reg_lo, reg_hi;
> > +
> > + pci_read_config_dword(pdev, i, &reg_lo);
> > + pci_read_config_dword(pdev, i + 4, &reg_hi);
> > +
> > + if (CXL_REGLOG_IS_MEMDEV(reg_lo)) {
> > + cxlm = cxl_mem_create(pdev, reg_lo, reg_hi);
> > + break;
> > + }
> > + }
> > +
> > + if (IS_ERR(cxlm))
> > + return -ENXIO;
>
> I think this would be easier to read if cxl_mem_create() returned NULL
> on failure (it prints error messages and we throw away
> -ENXIO/-ENOMEM distinction here anyway) so you could do:
>
> struct cxl_mem *cxlm = NULL;
>
> for (...) {
> if (...) {
> cxlm = cxl_mem_create(pdev, reg_lo, reg_hi);
> break;
> }
> }
>
> if (!cxlm)
> return -ENXIO; /* -ENODEV might be more natural? */
>

I agree on both counts. Both of these came from Dan, so I will let him explain.

> > - cxlm = devm_kzalloc(dev, sizeof(*cxlm), GFP_KERNEL);
> > - if (!cxlm)
> > - return -ENOMEM;
> > + pci_set_drvdata(pdev, cxlm);
> >
> > return 0;
> > }
> > diff --git a/drivers/cxl/pci.h b/drivers/cxl/pci.h
> > index beb03921e6da..be87f62e9132 100644
> > --- a/drivers/cxl/pci.h
> > +++ b/drivers/cxl/pci.h
> > @@ -12,4 +12,10 @@
> > #define PCI_DVSEC_ID_CXL 0x0
> > #define PCI_DVSEC_ID_CXL_REGLOC 0x8
> >
> > +#define CXL_REGLOG_RBI_EMPTY 0
> > +#define CXL_REGLOG_RBI_COMPONENT 1
> > +#define CXL_REGLOG_RBI_VIRT 2
> > +#define CXL_REGLOG_RBI_MEMDEV 3
>
> Maybe line these values up.
>
> > +#define CXL_REGLOG_IS_MEMDEV(x) ((((x) >> 8) & 0xff) == CXL_REGLOG_RBI_MEMDEV)
>
> If these are only needed in cxl/mem.c, they could go there. Do you
> expect code outside of drivers/cxl to need these?

Will do.

I'll suck in everything else as they seem like improvements.

>
> > #endif /* __CXL_PCI_H__ */
> > --
> > 2.29.2
> >