net: ipa: fix register write command validation

In ipa_cmd_register_write_valid() we verify that values we will
supply to a REGISTER_WRITE IPA immediate command will fit in
the fields that need to hold them.  This patch fixes some issues
in that function and ipa_cmd_register_write_offset_valid().

The dev_err() call in ipa_cmd_register_write_offset_valid() has
some printf format errors:
  - The name of the register (corresponding to the string format
    specifier) was not supplied.
  - The IPA base offset and offset need to be supplied separately to
    match the other format specifiers.
Also make the ~0 constant used there to compute the maximum
supported offset value explicitly unsigned.

There are two other issues in ipa_cmd_register_write_valid():
  - There's no need to check the hash flush register for platforms
    (like IPA v4.2) that do not support hashed tables
  - The highest possible endpoint number, whose status register
    offset is computed, is COUNT - 1, not COUNT.

Fix these problems, and add some additional commentary.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ipa/ipa_cmd.c

 // SPDX-License-Identifier: GPL-2.0
 
 /* Copyright (c) 2012-2018, The Linux Foundation. All rights reserved.
- * Copyright (C) 2019-2020 Linaro Ltd.
+ * Copyright (C) 2019-2021 Linaro Ltd.
  */
 
 #include <linux/types.h>
@@ -244,11 +244,15 @@ static bool ipa_cmd_register_write_offset_valid(struct ipa *ipa,
 	if (ipa->version != IPA_VERSION_3_5_1)
 		bit_count += hweight32(REGISTER_WRITE_FLAGS_OFFSET_HIGH_FMASK);
 	BUILD_BUG_ON(bit_count > 32);
-	offset_max = ~0 >> (32 - bit_count);
+	offset_max = ~0U >> (32 - bit_count);
 
+	/* Make sure the offset can be represented by the field(s)
+	 * that holds it.  Also make sure the offset is not outside
+	 * the overall IPA memory range.
+	 */
 	if (offset > offset_max || ipa->mem_offset > offset_max - offset) {
 		dev_err(dev, "%s offset too large 0x%04x + 0x%04x > 0x%04x)\n",
-				ipa->mem_offset + offset, offset_max);
+			name, ipa->mem_offset, offset, offset_max);
 		return false;
 	}
 
@@ -261,12 +265,24 @@ static bool ipa_cmd_register_write_valid(struct ipa *ipa)
 	const char *name;
 	u32 offset;
 
-	offset = ipa_reg_filt_rout_hash_flush_offset(ipa->version);
-	name = "filter/route hash flush";
-	if (!ipa_cmd_register_write_offset_valid(ipa, name, offset))
-		return false;
+	/* If hashed tables are supported, ensure the hash flush register
+	 * offset will fit in a register write IPA immediate command.
+	 */
+	if (ipa->version != IPA_VERSION_4_2) {
+		offset = ipa_reg_filt_rout_hash_flush_offset(ipa->version);
+		name = "filter/route hash flush";
+		if (!ipa_cmd_register_write_offset_valid(ipa, name, offset))
+			return false;
+	}
 
-	offset = IPA_REG_ENDP_STATUS_N_OFFSET(IPA_ENDPOINT_COUNT);
+	/* Each endpoint can have a status endpoint associated with it,
+	 * and this is recorded in an endpoint register.  If the modem
+	 * crashes, we reset the status endpoint for all modem endpoints
+	 * using a register write IPA immediate command.  Make sure the
+	 * worst case (highest endpoint number) offset of that endpoint
+	 * fits in the register write command field(s) that must hold it.
+	 */
+	offset = IPA_REG_ENDP_STATUS_N_OFFSET(IPA_ENDPOINT_COUNT - 1);
 	name = "maximal endpoint status";
 	if (!ipa_cmd_register_write_offset_valid(ipa, name, offset))
 		return false;