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.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hector Martin <marcan@marcan.st>

Author: marcan

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,
@@ -1684,11 +1692,32 @@ static int brcmf_pcie_download_fw_nvram(struct brcmf_pciedev_info *devinfo,
 	brcmf_pcie_write_ram32(devinfo, devinfo->ci->ramsize - 4, 0);
 
 	if (nvram) {
+		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;
+
 		brcmf_dbg(PCIE, "Download NVRAM %s\n", devinfo->nvram_name);
 		address = devinfo->ci->rambase + devinfo->ci->ramsize -
 			  nvram_len;
 		memcpy_toio(devinfo->tcm + address, nvram, nvram_len);
 		brcmf_fw_nvram_free(nvram);
+
+		/* 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);