[PATCH 1/4] PCI: endpoint: Add BAR_DISABLED and document BAR_RESERVED semantics

[Manikanta Maddireddy <mmaddireddy@nvidia.com>]

Add BAR_DISABLED to enum pci_epc_bar_type for BARs that are unused: the
EPC must disable them in .init(), the EPF must not use them, and they
are not returned by pci_epc_get_next_free_bar().

Document BAR_RESERVED for two uses: (1) HW-backed BARs (e.g. MSI-X
table, DMA regs) that the EPC may leave enabled for the host, and
(2) the second register of a 64-bit BAR (high 32 bits) when the
preceding BAR has only_64bit set.

Update pci_epc_get_next_free_bar() to treat both BAR_RESERVED and
BAR_DISABLED as not free so EPF drivers do not allocate or use
these BARs.

This allows EPC drivers such as Tegra194 to keep HW-backed 64-bit
BARs (MSI-X, DMA) enabled while still preventing EPF from using
reserved or disabled BARs.

Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
---
 drivers/pci/endpoint/pci-epc-core.c |  5 +++--
 include/linux/pci-epc.h             | 13 +++++++++++--
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
index ca7f19cc973a..1d6b04ac4fc5 100644
--- a/drivers/pci/endpoint/pci-epc-core.c
+++ b/drivers/pci/endpoint/pci-epc-core.c
@@ -103,8 +103,9 @@ enum pci_barno pci_epc_get_next_free_bar(const struct pci_epc_features
 		bar++;
 
 	for (i = bar; i < PCI_STD_NUM_BARS; i++) {
-		/* If the BAR is not reserved, return it. */
-		if (epc_features->bar[i].type != BAR_RESERVED)
+		/* If the BAR is not reserved or disabled, return it. */
+		if (epc_features->bar[i].type != BAR_RESERVED &&
+		    epc_features->bar[i].type != BAR_DISABLED)
 			return i;
 	}
 
diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
index 4286bfdbfdfa..9b3714a0dafc 100644
--- a/include/linux/pci-epc.h
+++ b/include/linux/pci-epc.h
@@ -191,13 +191,21 @@ struct pci_epc {
  * @BAR_RESIZABLE: The BAR implements the PCI-SIG Resizable BAR Capability.
  *		   NOTE: An EPC driver can currently only set a single supported
  *		   size.
- * @BAR_RESERVED: The BAR should not be touched by an EPF driver.
+ * @BAR_RESERVED: The BAR should not be touched by an EPF driver. Used for:
+ *		  (1) HW-backed BARs (e.g. MSI-X table, DMA regs) that the EPC
+ *		      may leave enabled for the host; (2) the second register
+ *		      of a 64-bit BAR (the high 32 bits), when the preceding
+ *		      BAR has only_64bit set.
+ * @BAR_DISABLED: The BAR is unused; the EPC must disable it in .init(); the
+ *		  EPF must not use it; it is not returned by
+ *		  pci_epc_get_next_free_bar().
  */
 enum pci_epc_bar_type {
 	BAR_PROGRAMMABLE = 0,
 	BAR_FIXED,
 	BAR_RESIZABLE,
 	BAR_RESERVED,
+	BAR_DISABLED,
 };
 
 /**
@@ -212,7 +220,8 @@ enum pci_epc_bar_type {
  *		only_64bit should not be set on a BAR of type BAR_RESERVED.
  *		(If BARx is a 64-bit BAR that an EPF driver is not allowed to
  *		touch, then both BARx and BARx+1 must be set to type
- *		BAR_RESERVED.)
+ *		BAR_RESERVED. BAR_RESERVED is used both for HW-backed BARs and
+ *		for the high half of a 64-bit BAR.)
  */
 struct pci_epc_bar_desc {
 	enum pci_epc_bar_type type;

-- 
2.34.1