[PATCH v8 2/6] PCI: add resizeable BAR infrastructure v5

[Christian KÃnig]

From: Christian KÃnig <christian.koenig@xxxxxxx>

Just the defines and helper functions to read the possible sizes of a BAR and
update it's size.

See https://pcisig.com/sites/default/files/specification_documents/ECN_Resizable-BAR_24Apr2008.pdf
and PCIe r3.1, sec 7.22.

This is useful for hardware with large local storage (mostly GFX) which only
expose 256MB BARs initially to be compatible with 32bit systems.

v2: provide read helper as well
v3: improve function names, use unsigned values, add better comments.
v4: move definition, improve commit message, s/bar/BAR/
v5: split out helper to find ctrl reg pos, style fixes, comment fixes,
    add pci_rbar_size_to_bytes as well

Signed-off-by: Christian KÃnig <christian.koenig@xxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
---
 drivers/pci/pci.c             | 104 ++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h             |   8 ++++
 include/uapi/linux/pci_regs.h |  11 ++++-
 3 files changed, 121 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d88edf5..647b799 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2957,6 +2957,110 @@ bool pci_acs_path_enabled(struct pci_dev *start,
 }
 
 /**
+ * pci_rbar_find_pos - find position of resize ctrl reg for BAR
+ * @dev: PCI device
+ * @bar: BAR to find
+ *
+ * Helper to find the postion of the ctrl register for a BAR.
+ * Returns -ENOTSUPP of resizeable BARs are not supported at all.
+ * Returns -ENOENT if not ctrl register for the BAR could be found.
+ */
+static int pci_rbar_find_pos(struct pci_dev *pdev, int bar)
+{
+	unsigned int pos, nbars;
+	unsigned int i;
+	u32 ctrl;
+
+	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);
+	if (!pos)
+		return -ENOTSUPP;
+
+	pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+	nbars = (ctrl & PCI_REBAR_CTRL_NBAR_MASK) >> PCI_REBAR_CTRL_NBAR_SHIFT;
+
+	for (i = 0; i < nbars; ++i, pos += 8) {
+		int bar_idx;
+
+		pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+		bar_idx = (ctrl & PCI_REBAR_CTRL_BAR_IDX_MASK) >>
+				PCI_REBAR_CTRL_BAR_IDX_SHIFT;
+		if (bar_idx == bar)
+			return pos;
+	}
+
+	return -ENOENT;
+}
+
+/**
+ * pci_rbar_get_possible_sizes - get possible sizes for BAR
+ * @dev: PCI device
+ * @bar: BAR to query
+ *
+ * Get the possible sizes of a resizeable BAR as bitmask defined in the spec
+ * (bit 0=1MB, bit 19=512GB). Returns 0 if BAR isn't resizeable.
+ */
+u32 pci_rbar_get_possible_sizes(struct pci_dev *pdev, int bar)
+{
+	u32 cap;
+	int pos;
+
+	pos = pci_rbar_find_pos(pdev, bar);
+	if (pos < 0)
+		return 0;
+
+	pci_read_config_dword(pdev, pos + PCI_REBAR_CAP, &cap);
+	return (cap & PCI_REBAR_CTRL_SIZES_MASK) >>
+		PCI_REBAR_CTRL_SIZES_SHIFT;
+}
+
+/**
+ * pci_rbar_get_current_size - get the current size of a BAR
+ * @dev: PCI device
+ * @bar: BAR to set size to
+ *
+ * Read the size of a BAR from the resizeable BAR config.
+ * Returns size if found or negative error code.
+ */
+int pci_rbar_get_current_size(struct pci_dev *pdev, int bar)
+{
+	u32 ctrl;
+	int pos;
+
+	pos = pci_rbar_find_pos(pdev, bar);
+	if (pos < 0)
+		return pos;
+
+	pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+	return (ctrl & PCI_REBAR_CTRL_BAR_SIZE_MASK) >>
+		PCI_REBAR_CTRL_BAR_SIZE_SHIFT;
+}
+
+/**
+ * pci_rbar_set_size - set a new size for a BAR
+ * @dev: PCI device
+ * @bar: BAR to set size to
+ * @size: new size as defined in the spec (0=1MB, 19=512GB)
+ *
+ * Set the new size of a BAR as defined in the spec.
+ * Returns zero if resizing was successful, error code otherwise.
+ */
+int pci_rbar_set_size(struct pci_dev *pdev, int bar, int size)
+{
+	u32 ctrl;
+	int pos;
+
+	pos = pci_rbar_find_pos(pdev, bar);
+	if (pos < 0)
+		return pos;
+
+	pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
+	ctrl &= ~PCI_REBAR_CTRL_BAR_SIZE_MASK;
+	ctrl |= size << PCI_REBAR_CTRL_BAR_SIZE_SHIFT;
+	pci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);
+	return 0;
+}
+
+/**
  * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
  * @dev: the PCI device
  * @pin: the INTx pin (1=INTA, 2=INTB, 3=INTC, 4=INTD)
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 136a0f9..e494f1e 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -367,4 +367,12 @@ int acpi_get_rc_resources(struct device *dev, const char *hid, u16 segment,
 			  struct resource *res);
 #endif
 
+u32 pci_rbar_get_possible_sizes(struct pci_dev *pdev, int bar);
+int pci_rbar_get_current_size(struct pci_dev *pdev, int bar);
+int pci_rbar_set_size(struct pci_dev *pdev, int bar, int size);
+static inline u64 pci_rbar_size_to_bytes(int size)
+{
+	return 1ULL << (size + 20);
+}
+
 #endif /* DRIVERS_PCI_H */
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index c22d3eb..d6a075d 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -943,9 +943,16 @@
 #define PCI_SATA_SIZEOF_LONG	16
 
 /* Resizable BARs */
+#define PCI_REBAR_CAP		4	/* capability register */
+#define  PCI_REBAR_CTRL_SIZES_MASK	(0xFFFFF << 4)	/* mask for sizes */
+#define  PCI_REBAR_CTRL_SIZES_SHIFT	4	/* shift for sizes */
 #define PCI_REBAR_CTRL		8	/* control register */
-#define  PCI_REBAR_CTRL_NBAR_MASK	(7 << 5)	/* mask for # bars */
-#define  PCI_REBAR_CTRL_NBAR_SHIFT	5	/* shift for # bars */
+#define  PCI_REBAR_CTRL_BAR_IDX_MASK	(7 << 0)	/* mask for BAR index */
+#define  PCI_REBAR_CTRL_BAR_IDX_SHIFT	0	/* shift for BAR index */
+#define  PCI_REBAR_CTRL_NBAR_MASK	(7 << 5)	/* mask for # BARs */
+#define  PCI_REBAR_CTRL_NBAR_SHIFT	5	/* shift for # BARs */
+#define  PCI_REBAR_CTRL_BAR_SIZE_MASK	(0x1F << 8)	/* mask for BAR size */
+#define  PCI_REBAR_CTRL_BAR_SIZE_SHIFT	8	/* shift for BAR size */
 
 /* Dynamic Power Allocation */
 #define PCI_DPA_CAP		4	/* capability register */
-- 
2.7.4