Re: [PATCH V5 3/4] crypto: Add Xilinx AES driver

From: Michal Simek
Date: Thu Jan 23 2020 - 07:10:44 EST


On 23. 01. 20 12:11, Kalyani Akula wrote:
> This patch adds AES driver support for the Xilinx ZynqMP SoC.
>
> Signed-off-by: Mohan Marutirao Dhanawade <mohan.dhanawade@xxxxxxxxxx>
> Signed-off-by: Kalyani Akula <kalyani.akula@xxxxxxxxxx>
> ---
>
> V5 Changes:
> - Replaced ARCH_ZYNQMP with ZYNQMP_FIRMWARE in Kconfig
> - Removed extra new lines.
> - Moved crypto: Add Xilinx AES driver patch from 4/4 to 3/4.
> - Updated Signed-off-by sequence.
>
> V4 Changes :
> - Addressed review comments.
>
> V3 Changes :
> - Added software fallback in cases where Hardware doesn't have
> the capability to handle the request.
> - Removed use of global variable for storing the driver data.
>
> V2 Changes :
> - Converted RFC PATCH to PATCH
> - Removed ALG_SET_KEY_TYPE that was added to support keytype
> attribute. Taken using setkey interface.
> - Removed deprecated BLKCIPHER in Kconfig
> - Erased Key/IV from the buffer.
> - Renamed zynqmp-aes driver to zynqmp-aes-gcm.
> - Addressed few other review comments
>
>
> drivers/crypto/Kconfig | 12 +
> drivers/crypto/Makefile | 1 +
> drivers/crypto/xilinx/Makefile | 2 +
> drivers/crypto/xilinx/zynqmp-aes-gcm.c | 466 +++++++++++++++++++++++++++++++++
> 4 files changed, 481 insertions(+)
> create mode 100644 drivers/crypto/xilinx/Makefile
> create mode 100644 drivers/crypto/xilinx/zynqmp-aes-gcm.c
>
> diff --git a/drivers/crypto/Kconfig b/drivers/crypto/Kconfig
> index 91eb768..f41e4eb 100644
> --- a/drivers/crypto/Kconfig
> +++ b/drivers/crypto/Kconfig
> @@ -676,6 +676,18 @@ config CRYPTO_DEV_ROCKCHIP
> This driver interfaces with the hardware crypto accelerator.
> Supporting cbc/ecb chainmode, and aes/des/des3_ede cipher mode.
>
> +config CRYPTO_DEV_ZYNQMP_AES
> + tristate "Support for Xilinx ZynqMP AES hw accelerator"
> + depends on ZYNQMP_FIRMWARE || COMPILE_TEST
> + select CRYPTO_AES
> + select CRYPTO_ENGINE
> + select CRYPTO_AEAD
> + help
> + Xilinx ZynqMP has AES-GCM engine used for symmetric key
> + encryption and decryption. This driver interfaces with AES hw
> + accelerator. Select this if you want to use the ZynqMP module
> + for AES algorithms.
> +
> config CRYPTO_DEV_MEDIATEK
> tristate "MediaTek's EIP97 Cryptographic Engine driver"
> depends on (ARM && ARCH_MEDIATEK) || COMPILE_TEST
> diff --git a/drivers/crypto/Makefile b/drivers/crypto/Makefile
> index 40229d4..d505d16 100644
> --- a/drivers/crypto/Makefile
> +++ b/drivers/crypto/Makefile
> @@ -47,5 +47,6 @@ obj-$(CONFIG_CRYPTO_DEV_VMX) += vmx/
> obj-$(CONFIG_CRYPTO_DEV_BCM_SPU) += bcm/
> obj-$(CONFIG_CRYPTO_DEV_SAFEXCEL) += inside-secure/
> obj-$(CONFIG_CRYPTO_DEV_ARTPEC6) += axis/
> +obj-$(CONFIG_CRYPTO_DEV_ZYNQMP_AES) += xilinx/
> obj-y += hisilicon/
> obj-$(CONFIG_CRYPTO_DEV_AMLOGIC_GXL) += amlogic/
> diff --git a/drivers/crypto/xilinx/Makefile b/drivers/crypto/xilinx/Makefile
> new file mode 100644
> index 0000000..534e32d
> --- /dev/null
> +++ b/drivers/crypto/xilinx/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_CRYPTO_DEV_ZYNQMP_AES) += zynqmp-aes-gcm.o
> diff --git a/drivers/crypto/xilinx/zynqmp-aes-gcm.c b/drivers/crypto/xilinx/zynqmp-aes-gcm.c
> new file mode 100644
> index 0000000..ca82da5
> --- /dev/null
> +++ b/drivers/crypto/xilinx/zynqmp-aes-gcm.c
> @@ -0,0 +1,466 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Xilinx ZynqMP AES Driver.
> + * Copyright (c) 2020 Xilinx Inc.
> + */
> +
> +#include <crypto/aes.h>
> +#include <crypto/engine.h>
> +#include <crypto/gcm.h>
> +#include <crypto/internal/aead.h>
> +#include <crypto/scatterwalk.h>
> +
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +
> +#include <linux/firmware/xlnx-zynqmp.h>
> +
> +#define ZYNQMP_DMA_BIT_MASK 32U
> +
> +#define ZYNQMP_AES_KEY_SIZE AES_KEYSIZE_256
> +#define ZYNQMP_AES_AUTH_SIZE 16U
> +#define ZYNQMP_KEY_SRC_SEL_KEY_LEN 1U
> +#define ZYNQMP_AES_BLK_SIZE 1U
> +#define ZYNQMP_AES_MIN_INPUT_BLK_SIZE 4U
> +#define ZYNQMP_AES_WORD_LEN 4U
> +
> +#define ZYNQMP_AES_GCM_TAG_MISMATCH_ERR 0x01
> +#define ZYNQMP_AES_WRONG_KEY_SRC_ERR 0x13
> +#define ZYNQMP_AES_PUF_NOT_PROGRAMMED 0xE300
> +
> +enum zynqmp_aead_op {
> + ZYNQMP_AES_DECRYPT = 0,
> + ZYNQMP_AES_ENCRYPT
> +};
> +
> +enum zynqmp_aead_keysrc {
> + ZYNQMP_AES_KUP_KEY = 0,
> + ZYNQMP_AES_DEV_KEY,
> + ZYNQMP_AES_PUF_KEY
> +};
> +
> +struct zynqmp_aead_drv_ctx {
> + union {
> + struct aead_alg aead;
> + } alg;
> + struct device *dev;
> + struct crypto_engine *engine;
> + const struct zynqmp_eemi_ops *eemi_ops;
> +};
> +
> +struct zynqmp_aead_hw_req {
> + u64 src;
> + u64 iv;
> + u64 key;
> + u64 dst;
> + u64 size;
> + u64 op;
> + u64 keysrc;
> +};
> +
> +struct zynqmp_aead_tfm_ctx {
> + struct crypto_engine_ctx engine_ctx;
> + struct device *dev;
> + u8 key[ZYNQMP_AES_KEY_SIZE];
> + u8 *iv;
> + u32 keylen;
> + u32 authsize;
> + enum zynqmp_aead_keysrc keysrc;
> + struct crypto_aead *fbk_cipher;
> +};
> +
> +struct zynqmp_aead_req_ctx {
> + enum zynqmp_aead_op op;
> +};
> +
> +static int zynqmp_aes_aead_cipher(struct aead_request *req)
> +{
> + struct crypto_aead *aead = crypto_aead_reqtfm(req);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx = crypto_aead_ctx(aead);
> + struct zynqmp_aead_req_ctx *rq_ctx = aead_request_ctx(req);
> + struct device *dev = tfm_ctx->dev;
> + struct aead_alg *alg = crypto_aead_alg(aead);
> + struct zynqmp_aead_drv_ctx *drv_ctx;
> + struct zynqmp_aead_hw_req *hwreq;
> + dma_addr_t dma_addr_data, dma_addr_hw_req;
> + unsigned int data_size;
> + unsigned int status;
> + size_t dma_size;
> + char *kbuf;
> + int err;
> +
> + drv_ctx = container_of(alg, struct zynqmp_aead_drv_ctx, alg.aead);
> +
> + if (!drv_ctx->eemi_ops->aes)
> + return -ENOTSUPP;
> +
> + if (tfm_ctx->keysrc == ZYNQMP_AES_KUP_KEY)
> + dma_size = req->cryptlen + ZYNQMP_AES_KEY_SIZE
> + + GCM_AES_IV_SIZE;
> + else
> + dma_size = req->cryptlen + GCM_AES_IV_SIZE;
> +
> + kbuf = dma_alloc_coherent(dev, dma_size, &dma_addr_data, GFP_KERNEL);
> + if (!kbuf)
> + return -ENOMEM;
> +
> + hwreq = dma_alloc_coherent(dev, sizeof(struct zynqmp_aead_hw_req),
> + &dma_addr_hw_req, GFP_KERNEL);
> + if (!hwreq) {
> + dma_free_coherent(dev, dma_size, kbuf, dma_addr_data);
> + return -ENOMEM;
> + }
> +
> + data_size = req->cryptlen;
> + scatterwalk_map_and_copy(kbuf, req->src, 0, req->cryptlen, 0);
> + memcpy(kbuf + data_size, req->iv, GCM_AES_IV_SIZE);
> +
> + hwreq->src = dma_addr_data;
> + hwreq->dst = dma_addr_data;
> + hwreq->iv = hwreq->src + data_size;
> + hwreq->keysrc = tfm_ctx->keysrc;
> + hwreq->op = rq_ctx->op;
> +
> + if (hwreq->op == ZYNQMP_AES_ENCRYPT)
> + hwreq->size = data_size;
> + else
> + hwreq->size = data_size - ZYNQMP_AES_AUTH_SIZE;
> +
> + if (hwreq->keysrc == ZYNQMP_AES_KUP_KEY) {
> + memcpy(kbuf + data_size + GCM_AES_IV_SIZE,
> + tfm_ctx->key, ZYNQMP_AES_KEY_SIZE);
> +
> + hwreq->key = hwreq->src + data_size + GCM_AES_IV_SIZE;
> + } else {
> + hwreq->key = 0;
> + }
> +
> + drv_ctx->eemi_ops->aes(dma_addr_hw_req, &status);
> +
> + if (status) {
> + switch (status) {
> + case ZYNQMP_AES_GCM_TAG_MISMATCH_ERR:
> + dev_err(dev, "ERROR: Gcm Tag mismatch\n");
> + break;
> + case ZYNQMP_AES_WRONG_KEY_SRC_ERR:
> + dev_err(dev, "ERROR: Wrong KeySrc, enable secure mode\n");
> + break;
> + case ZYNQMP_AES_PUF_NOT_PROGRAMMED:
> + dev_err(dev, "ERROR: PUF is not registered\n");
> + break;
> + default:
> + dev_err(dev, "ERROR: Unknown error\n");
> + break;
> + }
> + err = -status;
> + } else {
> + if (hwreq->op == ZYNQMP_AES_ENCRYPT)
> + data_size = data_size + ZYNQMP_AES_AUTH_SIZE;
> + else
> + data_size = data_size - ZYNQMP_AES_AUTH_SIZE;
> +
> + sg_copy_from_buffer(req->dst, sg_nents(req->dst),
> + kbuf, data_size);
> + err = 0;
> + }
> +
> + if (kbuf) {
> + memzero_explicit(kbuf, dma_size);
> + dma_free_coherent(dev, dma_size, kbuf, dma_addr_data);
> + }
> + if (hwreq) {
> + memzero_explicit(hwreq, sizeof(struct zynqmp_aead_hw_req));
> + dma_free_coherent(dev, sizeof(struct zynqmp_aead_hw_req),
> + hwreq, dma_addr_hw_req);
> + }
> + return err;
> +}
> +
> +static int zynqmp_fallback_check(struct zynqmp_aead_tfm_ctx *tfm_ctx,
> + struct aead_request *req)
> +{
> + int need_fallback = 0;
> + struct zynqmp_aead_req_ctx *rq_ctx = aead_request_ctx(req);
> +
> + if (tfm_ctx->authsize != ZYNQMP_AES_AUTH_SIZE)
> + need_fallback = 1;
> +
> + if (tfm_ctx->keysrc == ZYNQMP_AES_KUP_KEY &&
> + tfm_ctx->keylen != ZYNQMP_AES_KEY_SIZE) {
> + need_fallback = 1;
> + }
> + if (req->assoclen != 0 ||
> + req->cryptlen < ZYNQMP_AES_MIN_INPUT_BLK_SIZE) {
> + need_fallback = 1;
> + }
> + if ((req->cryptlen % ZYNQMP_AES_WORD_LEN) != 0)
> + need_fallback = 1;
> +
> + if (rq_ctx->op == ZYNQMP_AES_DECRYPT &&
> + req->cryptlen <= ZYNQMP_AES_AUTH_SIZE) {
> + need_fallback = 1;
> + }
> + return need_fallback;
> +}
> +
> +static int zynqmp_handle_aes_req(struct crypto_engine *engine,
> + void *req)
> +{
> + struct aead_request *areq =
> + container_of(req, struct aead_request, base);
> + struct crypto_aead *aead = crypto_aead_reqtfm(req);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx = crypto_aead_ctx(aead);
> + struct zynqmp_aead_req_ctx *rq_ctx = aead_request_ctx(areq);
> + struct aead_request *subreq = aead_request_ctx(req);
> + int need_fallback;
> + int err;
> +
> + need_fallback = zynqmp_fallback_check(tfm_ctx, areq);
> +
> + if (need_fallback) {
> + aead_request_set_tfm(subreq, tfm_ctx->fbk_cipher);
> +
> + aead_request_set_callback(subreq, areq->base.flags,
> + NULL, NULL);
> + aead_request_set_crypt(subreq, areq->src, areq->dst,
> + areq->cryptlen, areq->iv);
> + aead_request_set_ad(subreq, areq->assoclen);
> + if (rq_ctx->op == ZYNQMP_AES_ENCRYPT)
> + err = crypto_aead_encrypt(subreq);
> + else
> + err = crypto_aead_decrypt(subreq);
> + } else {
> + err = zynqmp_aes_aead_cipher(areq);
> + }
> +
> + crypto_finalize_aead_request(engine, areq, err);
> + return 0;
> +}
> +
> +static int zynqmp_aes_aead_setkey(struct crypto_aead *aead, const u8 *key,
> + unsigned int keylen)
> +{
> + struct crypto_tfm *tfm = crypto_aead_tfm(aead);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx =
> + (struct zynqmp_aead_tfm_ctx *)crypto_tfm_ctx(tfm);
> + unsigned char keysrc;
> + int err;
> +
> + if (keylen == ZYNQMP_KEY_SRC_SEL_KEY_LEN) {
> + keysrc = *key;
> + if (keysrc == ZYNQMP_AES_KUP_KEY ||
> + keysrc == ZYNQMP_AES_DEV_KEY ||
> + keysrc == ZYNQMP_AES_PUF_KEY) {
> + tfm_ctx->keysrc = (enum zynqmp_aead_keysrc)keysrc;
> + } else {
> + tfm_ctx->keylen = keylen;
> + }
> + } else {
> + tfm_ctx->keylen = keylen;
> + if (keylen == ZYNQMP_AES_KEY_SIZE) {
> + tfm_ctx->keysrc = ZYNQMP_AES_KUP_KEY;
> + memcpy(tfm_ctx->key, key, keylen);
> + }
> + }
> +
> + tfm_ctx->fbk_cipher->base.crt_flags &= ~CRYPTO_TFM_REQ_MASK;
> + tfm_ctx->fbk_cipher->base.crt_flags |= (aead->base.crt_flags &
> + CRYPTO_TFM_REQ_MASK);
> +
> + err = crypto_aead_setkey(tfm_ctx->fbk_cipher, key, keylen);
> + if (err) {
> + aead->base.crt_flags &= ~CRYPTO_TFM_RES_MASK;
> + aead->base.crt_flags |=
> + (tfm_ctx->fbk_cipher->base.crt_flags &
> + CRYPTO_TFM_RES_MASK);
> + }
> +
> + return err;
> +}
> +
> +static int zynqmp_aes_aead_setauthsize(struct crypto_aead *aead,
> + unsigned int authsize)
> +{
> + struct crypto_tfm *tfm = crypto_aead_tfm(aead);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx =
> + (struct zynqmp_aead_tfm_ctx *)crypto_tfm_ctx(tfm);
> +
> + tfm_ctx->authsize = authsize;
> + return crypto_aead_setauthsize(tfm_ctx->fbk_cipher, authsize);
> +}
> +
> +static int zynqmp_aes_aead_encrypt(struct aead_request *req)
> +{
> + struct zynqmp_aead_drv_ctx *drv_ctx;
> + struct crypto_aead *aead = crypto_aead_reqtfm(req);
> + struct aead_alg *alg = crypto_aead_alg(aead);
> + struct zynqmp_aead_req_ctx *rq_ctx = aead_request_ctx(req);
> +
> + rq_ctx->op = ZYNQMP_AES_ENCRYPT;
> + drv_ctx = container_of(alg, struct zynqmp_aead_drv_ctx, alg.aead);
> +
> + return crypto_transfer_aead_request_to_engine(drv_ctx->engine, req);
> +}
> +
> +static int zynqmp_aes_aead_decrypt(struct aead_request *req)
> +{
> + struct zynqmp_aead_drv_ctx *drv_ctx;
> + struct crypto_aead *aead = crypto_aead_reqtfm(req);
> + struct aead_alg *alg = crypto_aead_alg(aead);
> + struct zynqmp_aead_req_ctx *rq_ctx = aead_request_ctx(req);
> +
> + rq_ctx->op = ZYNQMP_AES_DECRYPT;
> + drv_ctx = container_of(alg, struct zynqmp_aead_drv_ctx, alg.aead);
> +
> + return crypto_transfer_aead_request_to_engine(drv_ctx->engine, req);
> +}
> +
> +static int zynqmp_aes_aead_init(struct crypto_aead *aead)
> +{
> + struct crypto_tfm *tfm = crypto_aead_tfm(aead);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx =
> + (struct zynqmp_aead_tfm_ctx *)crypto_tfm_ctx(tfm);
> + struct zynqmp_aead_drv_ctx *drv_ctx;
> + struct aead_alg *alg = crypto_aead_alg(aead);
> +
> + drv_ctx = container_of(alg, struct zynqmp_aead_drv_ctx, alg.aead);
> + tfm_ctx->dev = drv_ctx->dev;
> +
> + tfm_ctx->engine_ctx.op.do_one_request = zynqmp_handle_aes_req;
> + tfm_ctx->engine_ctx.op.prepare_request = NULL;
> + tfm_ctx->engine_ctx.op.unprepare_request = NULL;
> +
> + tfm_ctx->fbk_cipher = crypto_alloc_aead(drv_ctx->alg.aead.base.cra_name,
> + 0,
> + CRYPTO_ALG_NEED_FALLBACK);
> +
> + if (IS_ERR(tfm_ctx->fbk_cipher)) {
> + pr_err("%s() Error: failed to allocate fallback for %s\n",
> + __func__, drv_ctx->alg.aead.base.cra_name);
> + return PTR_ERR(tfm_ctx->fbk_cipher);
> + }
> +
> + crypto_aead_set_reqsize(aead,
> + max(sizeof(struct zynqmp_aead_req_ctx),
> + sizeof(struct aead_request) +
> + crypto_aead_reqsize(tfm_ctx->fbk_cipher)));
> + return 0;
> +}
> +
> +static void zynqmp_aes_aead_exit(struct crypto_aead *aead)
> +{
> + struct crypto_tfm *tfm = crypto_aead_tfm(aead);
> + struct zynqmp_aead_tfm_ctx *tfm_ctx =
> + (struct zynqmp_aead_tfm_ctx *)crypto_tfm_ctx(tfm);
> +
> + if (tfm_ctx->fbk_cipher) {
> + crypto_free_aead(tfm_ctx->fbk_cipher);
> + tfm_ctx->fbk_cipher = NULL;
> + }
> + memzero_explicit(tfm_ctx, sizeof(struct zynqmp_aead_tfm_ctx));
> +}
> +
> +static struct zynqmp_aead_drv_ctx aes_drv_ctx = {
> + .alg.aead = {
> + .setkey = zynqmp_aes_aead_setkey,
> + .setauthsize = zynqmp_aes_aead_setauthsize,
> + .encrypt = zynqmp_aes_aead_encrypt,
> + .decrypt = zynqmp_aes_aead_decrypt,
> + .init = zynqmp_aes_aead_init,
> + .exit = zynqmp_aes_aead_exit,
> + .ivsize = GCM_AES_IV_SIZE,
> + .maxauthsize = ZYNQMP_AES_AUTH_SIZE,
> + .base = {
> + .cra_name = "gcm(aes)",
> + .cra_driver_name = "xilinx-zynqmp-aes-gcm",
> + .cra_priority = 200,
> + .cra_flags = CRYPTO_ALG_TYPE_AEAD |
> + CRYPTO_ALG_ASYNC |
> + CRYPTO_ALG_KERN_DRIVER_ONLY |
> + CRYPTO_ALG_NEED_FALLBACK,
> + .cra_blocksize = ZYNQMP_AES_BLK_SIZE,
> + .cra_ctxsize = sizeof(struct zynqmp_aead_tfm_ctx),
> + .cra_module = THIS_MODULE,
> + }
> + }
> +};
> +
> +static int zynqmp_aes_aead_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + int err;
> +
> + /* ZynqMP AES driver supports only one instance */
> + if (!aes_drv_ctx.dev)
> + aes_drv_ctx.dev = dev;
> + else
> + return -ENODEV;
> +
> + aes_drv_ctx.eemi_ops = zynqmp_pm_get_eemi_ops();
> + if (IS_ERR(aes_drv_ctx.eemi_ops)) {
> + dev_err(dev, "Failed to get ZynqMP EEMI interface\n");
> + return PTR_ERR(aes_drv_ctx.eemi_ops);
> + }
> +
> + err = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(ZYNQMP_DMA_BIT_MASK));
> + if (err < 0) {
> + dev_err(dev, "No usable DMA configuration\n");
> + return err;
> + }
> +
> + aes_drv_ctx.engine = crypto_engine_alloc_init(dev, 1);
> + if (!aes_drv_ctx.engine) {
> + dev_err(dev, "Cannot alloc AES engine\n");
> + err = -ENOMEM;
> + goto err_engine;
> + }
> +
> + err = crypto_engine_start(aes_drv_ctx.engine);
> + if (err) {
> + dev_err(dev, "Cannot start AES engine\n");
> + goto err_engine;
> + }
> +
> + err = crypto_register_aead(&aes_drv_ctx.alg.aead);
> + if (err < 0) {
> + dev_err(dev, "Failed to register AEAD alg.\n");
> + goto err_aead;
> + }
> + return 0;
> +
> +err_aead:
> + crypto_unregister_aead(&aes_drv_ctx.alg.aead);
> +
> +err_engine:
> + if (aes_drv_ctx.engine)
> + crypto_engine_exit(aes_drv_ctx.engine);
> +
> + return err;
> +}
> +
> +static int zynqmp_aes_aead_remove(struct platform_device *pdev)
> +{
> + crypto_engine_exit(aes_drv_ctx.engine);
> + crypto_unregister_aead(&aes_drv_ctx.alg.aead);
> +
> + return 0;
> +}
> +
> +static const struct of_device_id zynqmp_aes_dt_ids[] = {
> + { .compatible = "xlnx,zynqmp-aes" },
> + { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, zynqmp_aes_dt_ids);
> +
> +static struct platform_driver zynqmp_aes_driver = {
> + .probe = zynqmp_aes_aead_probe,
> + .remove = zynqmp_aes_aead_remove,
> + .driver = {
> + .name = "zynqmp-aes",
> + .of_match_table = zynqmp_aes_dt_ids,
> + },
> +};
> +
> +module_platform_driver(zynqmp_aes_driver);
> +MODULE_LICENSE("GPL");
>

Herbert: I can't see any issue with this driver but I checked only
common parts.
1/4 is based on one patch merged to soc queue for v5.6 (links around).
It means there is really dependency on it. If you want me to deal with
that please let me know.

Acked-by: Michal Simek <michal.simek@xxxxxxxxxx>

Thanks,
Michal