wifi: brcmfmac: pcie: Provide a buffer of random bytes to the device

Newer Apple firmwares on chipsets without a hardware RNG require the
host to provide a buffer of 256 random bytes to the device on
initialization. This buffer is present immediately before NVRAM,
suffixed by a footer containing a magic number and the buffer length.

This won't affect chips/firmwares that do not use this feature, so do it
unconditionally for all Apple platforms (those with an Apple OTP).
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230214080034.3828-3-marcan@marcan.st

drivers/net/wireless/broadcom/brcm80211/brcmfmac/pcie.c

@@ -15,6 +15,7 @@
 #include <linux/sched/signal.h>
 #include <linux/kthread.h>
 #include <linux/io.h>
+#include <linux/random.h>
 #include <asm/unaligned.h>
 
 #include <soc.h>
@@ -1653,6 +1654,13 @@ brcmf_pcie_init_share_ram_info(struct brcmf_pciedev_info *devinfo,
 	return 0;
 }
 
+struct brcmf_random_seed_footer {
+	__le32 length;
+	__le32 magic;
+};
+
+#define BRCMF_RANDOM_SEED_MAGIC		0xfeedc0de
+#define BRCMF_RANDOM_SEED_LENGTH	0x100
 
 static int brcmf_pcie_download_fw_nvram(struct brcmf_pciedev_info *devinfo,
 					const struct firmware *fw, void *nvram,
@@ -1689,6 +1697,30 @@ static int brcmf_pcie_download_fw_nvram(struct brcmf_pciedev_info *devinfo,
 			  nvram_len;
 		memcpy_toio(devinfo->tcm + address, nvram, nvram_len);
 		brcmf_fw_nvram_free(nvram);
+
+		if (devinfo->otp.valid) {
+			size_t rand_len = BRCMF_RANDOM_SEED_LENGTH;
+			struct brcmf_random_seed_footer footer = {
+				.length = cpu_to_le32(rand_len),
+				.magic = cpu_to_le32(BRCMF_RANDOM_SEED_MAGIC),
+			};
+			void *randbuf;
+
+			/* Some Apple chips/firmwares expect a buffer of random
+			 * data to be present before NVRAM
+			 */
+			brcmf_dbg(PCIE, "Download random seed\n");
+
+			address -= sizeof(footer);
+			memcpy_toio(devinfo->tcm + address, &footer,
+				    sizeof(footer));
+
+			address -= rand_len;
+			randbuf = kzalloc(rand_len, GFP_KERNEL);
+			get_random_bytes(randbuf, rand_len);
+			memcpy_toio(devinfo->tcm + address, randbuf, rand_len);
+			kfree(randbuf);
+		}
 	} else {
 		brcmf_dbg(PCIE, "No matching NVRAM file found %s\n",
 			  devinfo->nvram_name);