nfp: support long reads and writes with the cpp helpers

nfp_cpp_{read,write}() helpers perform device memory mapping (setting
the PCIe -> NOC translation BARs) and accessing it.  They, however,
currently implicitly expect that the length of entire operation will
fit in one BAR translation window.  There is a number of 16MB windows
available, and we don't really need to access such large areas today.

If the user, however, manages to trick the driver into making a big
mapping (e.g. by providing a huge fake FW file), the driver will
print a warning saying "No suitable BAR found for request" and a
stack trace - which most users find concerning.

To be future-proof and not scare users with warnings, make the
nfp_cpp_{read,write}() helpers do accesses chunk by chunk if the area
size is large.  Set the notion of "large" to 2MB, which is the size
of the smallest BAR window.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfpcore/nfp_cpp.h

@@ -42,6 +42,7 @@
 
 #include <linux/ctype.h>
 #include <linux/types.h>
+#include <linux/sizes.h>
 
 #ifndef NFP_SUBSYS
 #define NFP_SUBSYS "nfp"
@@ -59,6 +60,8 @@
 #define PCI_64BIT_BAR_COUNT             3
 
 #define NFP_CPP_NUM_TARGETS             16
+/* Max size of area it should be safe to request */
+#define NFP_CPP_SAFE_AREA_SIZE		SZ_2M
 
 struct device;
 

drivers/net/ethernet/netronome/nfp/nfpcore/nfp_cppcore.c

@@ -924,18 +924,9 @@ area_cache_put(struct nfp_cpp *cpp, struct nfp_cpp_area_cache *cache)
 	mutex_unlock(&cpp->area_cache_mutex);
 }
 
-/**
- * nfp_cpp_read() - read from CPP target
- * @cpp:		CPP handle
- * @destination:	CPP id
- * @address:		offset into CPP target
- * @kernel_vaddr:	kernel buffer for result
- * @length:		number of bytes to read
- *
- * Return: length of io, or -ERRNO
- */
-int nfp_cpp_read(struct nfp_cpp *cpp, u32 destination,
-		 unsigned long long address, void *kernel_vaddr, size_t length)
+static int __nfp_cpp_read(struct nfp_cpp *cpp, u32 destination,
+			  unsigned long long address, void *kernel_vaddr,
+			  size_t length)
 {
 	struct nfp_cpp_area_cache *cache;
 	struct nfp_cpp_area *area;
@@ -968,18 +959,43 @@ int nfp_cpp_read(struct nfp_cpp *cpp, u32 destination,
 }
 
 /**
- * nfp_cpp_write() - write to CPP target
+ * nfp_cpp_read() - read from CPP target
  * @cpp:		CPP handle
  * @destination:	CPP id
  * @address:		offset into CPP target
- * @kernel_vaddr:	kernel buffer to read from
- * @length:		number of bytes to write
+ * @kernel_vaddr:	kernel buffer for result
+ * @length:		number of bytes to read
  *
  * Return: length of io, or -ERRNO
  */
-int nfp_cpp_write(struct nfp_cpp *cpp, u32 destination,
-		  unsigned long long address,
-		  const void *kernel_vaddr, size_t length)
+int nfp_cpp_read(struct nfp_cpp *cpp, u32 destination,
+		 unsigned long long address, void *kernel_vaddr,
+		 size_t length)
+{
+	size_t n, offset;
+	int ret;
+
+	for (offset = 0; offset < length; offset += n) {
+		unsigned long long r_addr = address + offset;
+
+		/* make first read smaller to align to safe window */
+		n = min_t(size_t, length - offset,
+			  ALIGN(r_addr + 1, NFP_CPP_SAFE_AREA_SIZE) - r_addr);
+
+		ret = __nfp_cpp_read(cpp, destination, address + offset,
+				     kernel_vaddr + offset, n);
+		if (ret < 0)
+			return ret;
+		if (ret != n)
+			return offset + n;
+	}
+
+	return length;
+}
+
+static int __nfp_cpp_write(struct nfp_cpp *cpp, u32 destination,
+			   unsigned long long address,
+			   const void *kernel_vaddr, size_t length)
 {
 	struct nfp_cpp_area_cache *cache;
 	struct nfp_cpp_area *area;
@@ -1011,6 +1027,41 @@ int nfp_cpp_write(struct nfp_cpp *cpp, u32 destination,
 	return err;
 }
 
+/**
+ * nfp_cpp_write() - write to CPP target
+ * @cpp:		CPP handle
+ * @destination:	CPP id
+ * @address:		offset into CPP target
+ * @kernel_vaddr:	kernel buffer to read from
+ * @length:		number of bytes to write
+ *
+ * Return: length of io, or -ERRNO
+ */
+int nfp_cpp_write(struct nfp_cpp *cpp, u32 destination,
+		  unsigned long long address,
+		  const void *kernel_vaddr, size_t length)
+{
+	size_t n, offset;
+	int ret;
+
+	for (offset = 0; offset < length; offset += n) {
+		unsigned long long w_addr = address + offset;
+
+		/* make first write smaller to align to safe window */
+		n = min_t(size_t, length - offset,
+			  ALIGN(w_addr + 1, NFP_CPP_SAFE_AREA_SIZE) - w_addr);
+
+		ret = __nfp_cpp_write(cpp, destination, address + offset,
+				      kernel_vaddr + offset, n);
+		if (ret < 0)
+			return ret;
+		if (ret != n)
+			return offset + n;
+	}
+
+	return length;
+}
+
 /* Return the correct CPP address, and fixup xpb_addr as needed. */
 static u32 nfp_xpb_to_cpp(struct nfp_cpp *cpp, u32 *xpb_addr)
 {