[PATCH v2] RISC-V: Add PCIe I/O BAR memory mapping

[Yash Shah]

For legacy I/O BARs (non-MMIO BARs) to work correctly on RISC-V Linux,
we need to establish a reserved memory region for them, so that drivers
that wish to use the legacy I/O BARs can issue reads and writes against
a memory region that is mapped to the host PCIe controller's I/O BAR
mapping.

Signed-off-by: Yash Shah <yash.shah@xxxxxxxxxx>
---

Changes in v2:
- update patch description as per Paul's suggestion
https://lore.kernel.org/linux-riscv/alpine.DEB.2.21.9999.1910240937350.20010@xxxxxxxxxxxxxxxx/

---
 arch/riscv/include/asm/io.h      | 7 +++++++
 arch/riscv/include/asm/pgtable.h | 7 ++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
index fc1189a..3ba4d93 100644
--- a/arch/riscv/include/asm/io.h
+++ b/arch/riscv/include/asm/io.h
@@ -13,6 +13,7 @@
 
 #include <linux/types.h>
 #include <asm/mmiowb.h>
+#include <asm/pgtable.h>
 
 extern void __iomem *ioremap(phys_addr_t offset, unsigned long size);
 
@@ -162,6 +163,12 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
 #endif
 
 /*
+ *  I/O port access constants.
+ */
+#define IO_SPACE_LIMIT		(PCI_IO_SIZE - 1)
+#define PCI_IOBASE		((void __iomem *)PCI_IO_START)
+
+/*
  * Emulation routines for the port-mapped IO space used by some PCI drivers.
  * These are defined as being "fully synchronous", but also "not guaranteed to
  * be fully ordered with respect to other memory and I/O operations".  We're
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 7fc5e4a..d78cc74 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -7,6 +7,7 @@
 #define _ASM_RISCV_PGTABLE_H
 
 #include <linux/mmzone.h>
+#include <linux/sizes.h>
 
 #include <asm/pgtable-bits.h>
 
@@ -88,6 +89,7 @@ extern pgd_t swapper_pg_dir[];
 #define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
 #define VMALLOC_END      (PAGE_OFFSET - 1)
 #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
+#define PCI_IO_SIZE      SZ_16M
 
 /*
  * Roughly size the vmemmap space to be large enough to fit enough
@@ -102,7 +104,10 @@ extern pgd_t swapper_pg_dir[];
 
 #define vmemmap		((struct page *)VMEMMAP_START)
 
-#define FIXADDR_TOP      (VMEMMAP_START)
+#define PCI_IO_END       VMEMMAP_START
+#define PCI_IO_START     (PCI_IO_END - PCI_IO_SIZE)
+#define FIXADDR_TOP      PCI_IO_START
+
 #ifdef CONFIG_64BIT
 #define FIXADDR_SIZE     PMD_SIZE
 #else
-- 
2.7.4