SchOS/ldls/kpi/pci.c

// SPDX-License-Identifier: GPL-2.0-or-later
//
// The PCI half of the KPI. See ldls/kpi/kpi.h for the provenance rule.
//
// Every one of these lands on `/dev/pci`, which is the interface
// docs/plan/hybrid.md built and `vgpud` proved. That it fits a foreign driver
// without alteration is the point the hybrid plan was making when it insisted
// the interface be about *PCI devices* rather than about a driver model:
//
//   "an interface whose first consumers are native drivers is a general
//    mechanism that something foreign can use later, rather than a hole shaped
//    like something foreign."
//
// This file is that claim being collected.

#include "core/types.h"
#include "uapi/user.h"
#include "uapi/fcntl.h"
#include "uapi/posix.h"
#include "dev/pciuser.h"
#include "kpi.h"

// The PCI resource flag bits, which are ABI between the kernel and every
// driver written against it. Not layout, so BTF does not carry them.
#define LDLS_IORESOURCE_IO  0x00000100
#define LDLS_IORESOURCE_MEM 0x00000200

// The device is claimed by the host before the driver runs, because claiming
// is what enables memory space and bus mastering -- and a BAR read before that
// can legitimately be zero. So by the time a driver calls this, it has already
// happened, and the honest answer is success.
int
kpi_pci_enable_device(void *pdev)
{
  (void)pdev;
  return 0;
}

// Regions are not reserved against anyone: this process holds the whole
// device, exclusively, because /dev/pci gives out one device per process.
// There is nobody to arbitrate with.
int
kpi_pci_request_regions(void *pdev, const char *name)
{
  (void)pdev; (void)name;
  return 0;
}

void
kpi_pci_release_regions(void *pdev)
{
  (void)pdev;
}

// Also already done, by PCIIOC_CLAIM, which sets PCI_CMD_MEMORY and
// PCI_CMD_BUS_MASTER together -- see do_claim() in kernel/dev/pciuser.c, and
// the comment there about why a driver that has to ask separately will forget.
void
kpi_pci_set_master(void *pdev)
{
  (void)pdev;
}

int
kpi_pci_read_config_word(void *pdev, int where, unsigned short *v)
{
  struct pciuser_cfg c;

  (void)pdev;
  c.index  = (unsigned int)kpi.index;
  c.offset = (unsigned int)where & ~3u;
  c.value  = 0;
  if (ioctl(kpi.pcifd, PCIIOC_CFG, &c) < 0)
    return -1;
  if (v)
    *v = (unsigned short)(c.value >> ((where & 2) * 8));
  return 0;
}

// Refused, deliberately and loudly.
//
// /dev/pci has no config *write* at all, and that is the line that matters:
// a write is how a BAR gets moved out from under the kernel. A driver that
// needs one has found a real limit of this interface rather than a bug, and
// silently succeeding would turn that into a mystery somewhere else.
int
kpi_pci_write_config_word(void *pdev, int where, unsigned short v)
{
  (void)pdev; (void)v;
  kpi_log("kpi: the driver tried to WRITE config space at 0x");
  kpi_loghex((unsigned long long)where, 2);
  kpi_log(" -- /dev/pci does not allow that\n");
  return -1;
}

// Map a BAR.
//
// The offset passed to mmap is the BAR's *physical address*, which is what
// makes the kernel able to check it: an offset that is not inside a BAR of a
// device this process holds is refused, and that check is the whole difference
// between /dev/pci and /dev/mem with extra steps.
void *
kpi_pci_iomap(void *pdev, int bar, unsigned long max)
{
  unsigned long long len;
  void *p;

  (void)pdev;
  if (bar < 0 || bar >= 6 || kpi.bar_base[bar] == 0) {
    kpi_log("kpi: pci_iomap of BAR "); kpi_lognum(bar);
    kpi_log(", which this device does not have\n");
    return 0;
  }

  // An I/O-space BAR has no address to map. rtl8139 offers both and its driver
  // prefers MMIO when it can get it; saying no here is what makes it take that
  // path rather than issuing port instructions a process cannot execute.
  if (kpi.bar_flags[bar] & PCIUSER_BAR_IO) {
    kpi_log("kpi: BAR "); kpi_lognum(bar);
    kpi_log(" is I/O space, which cannot be mapped\n");
    return 0;
  }

  len = kpi.bar_size[bar];
  if (max && max < len)
    len = max;

  p = mmap(0, len, PROT_READ | PROT_WRITE, MAP_SHARED, kpi.pcifd,
           kpi.bar_base[bar]);

  // Any small negative is an error, not an address.
  //
  // SchOS returns -errno from mmap rather than MAP_FAILED, so checking only
  // for -1 lets every other failure through as a pointer. That is not a
  // theoretical worry: this returned -EACCES, the driver took -13 as its
  // register base, and the first write landed at 0x4e -- thirteen below where
  // it meant to be, which is how the real fault below was eventually found.
  if (p == 0 || ((long)p < 0 && (long)p > -4096)) {
    kpi_log("kpi: the kernel refused to map BAR "); kpi_lognum(bar);
    kpi_log(", error "); kpi_lognum(-(long)p); kpi_log("\n");
    return 0;
  }

  kpi.io_base = (unsigned long)p;
  kpi.io_len  = len;

  kpi_log("  kpi: mapped BAR "); kpi_lognum(bar);
  kpi_log(" -- phys 0x"); kpi_loghex(kpi.bar_base[bar], 16);
  kpi_log(", "); kpi_lognum((long long)len); kpi_log(" bytes\n");
  return p;
}

// pci_ioremap_bar(pdev, bar) -- the same thing as pci_iomap with no cap. A
// second spelling, which is the sort of thing a second driver turns up.
void *
kpi_pci_ioremap_bar(void *pdev, int bar)
{
  return kpi_pci_iomap(pdev, bar, 0);
}

// pci_select_bars(pdev, flags) -- which BARs match a resource kind.
//
// A driver asks this before requesting regions, so the answer decides which
// BARs it thinks exist. Reporting one that is not there gets it refused later;
// omitting one it needs gets it to give up here.
int
kpi_pci_select_bars(void *pdev, unsigned long flags)
{
  int bars = 0, b;

  (void)pdev;
  for (b = 0; b < 6; b++) {
    if (!kpi.bar_base[b])
      continue;
    if ((kpi.bar_flags[b] & PCIUSER_BAR_IO)  && (flags & LDLS_IORESOURCE_IO))
      bars |= 1 << b;
    if ((kpi.bar_flags[b] & PCIUSER_BAR_MMIO) && (flags & LDLS_IORESOURCE_MEM))
      bars |= 1 << b;
  }
  return bars;
}

int
kpi_pci_request_selected_regions(void *pdev, int bars, const char *name)
{
  (void)pdev; (void)bars; (void)name;
  return 0;                        // nobody to arbitrate with; see above
}

void
kpi_pci_release_selected_regions(void *pdev, int bars)
{
  (void)pdev; (void)bars;
}

// Saving and restoring config space is what a driver does around a reset it
// expects to clear the BARs. LDLS never resets the device at that level and
// has no config write to restore with, so there is nothing to save -- and
// saying so by succeeding is right, because a driver that cannot save state
// refuses to probe at all.
int  kpi_pci_save_state(void *pdev)    { (void)pdev; return 0; }
void kpi_pci_restore_state(void *pdev) { (void)pdev; }

void
kpi_pci_iounmap(void *pdev, void *addr)
{
  (void)pdev; (void)addr;
}