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Message-ID:
<PAXPR04MB9448D64AC3748909BE87A19FF4522@PAXPR04MB9448.eurprd04.prod.outlook.com>
Date: Tue, 5 Nov 2024 14:05:42 +0000
From: Sandor Yu <sandor.yu@....com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: "andrzej.hajda@...el.com" <andrzej.hajda@...el.com>,
"neil.armstrong@...aro.org" <neil.armstrong@...aro.org>, Laurent Pinchart
<laurent.pinchart@...asonboard.com>, "jonas@...boo.se" <jonas@...boo.se>,
"jernej.skrabec@...il.com" <jernej.skrabec@...il.com>, "airlied@...il.com"
<airlied@...il.com>, "daniel@...ll.ch" <daniel@...ll.ch>,
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"vkoul@...nel.org" <vkoul@...nel.org>, "dri-devel@...ts.freedesktop.org"
<dri-devel@...ts.freedesktop.org>, "devicetree@...r.kernel.org"
<devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-phy@...ts.infradead.org"
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"sam@...nborg.org" <sam@...nborg.org>
Subject: Re: [PATCH v18 1/8] drm: bridge: Cadence: Create MHDP helper driver
>
> On Tue, Oct 29, 2024 at 02:02:09PM +0800, Sandor Yu wrote:
> > Mailbox access functions in MHDP8546 will be share to other MHDP
> > driver and Cadence HDP-TX HDMI/DP PHY drivers.
> >
> > Create a new MHDP helper driver and move all mailbox access functions
> into.
> > According the mailbox access sequence and type of security.
> > Six mailbox access API functions are introduced.
> > Three APIs for non-secure mailbox access:
> > - cdns_mhdp_mailbox_send()
> > - cdns_mhdp_mailbox_send_recv()
> > - cdns_mhdp_mailbox_send_recv_multi()
> > The other three APIs for secure mailbox access:
> > - cdns_mhdp_secure_mailbox_send()
> > - cdns_mhdp_secure_mailbox_send_recv()
> > - cdns_mhdp_secure_mailbox_send_recv_multi()
> >
> > All MHDP commands that need to be passed through the mailbox have been
> > rewritten using those new API functions.
> >
> > The register read/write and DP DPCD read/write command functions are
> > also included in this new helper driver.
> >
> > Function cdns_mhdp_reg_write() is renamed to cdns_mhdp_dp_reg_write(),
> > because it use the DPTX command ID DPTX_WRITE_REGISTER.
> > New cdns_mhdp_reg_write() is added with the general command ID
> > GENERAL_REGISTER_WRITE.
> >
> > Signed-off-by: Sandor Yu <Sandor.yu@....com>
> > ---
> > v17->v18:
> > - Create three ordinary mailbox access APIs
> > cdns_mhdp_mailbox_send
> > cdns_mhdp_mailbox_send_recv
> > cdns_mhdp_mailbox_send_recv_multi
> > - Create three secure mailbox access APIs
> > cdns_mhdp_secure_mailbox_send
> > cdns_mhdp_secure_mailbox_send_recv
> > cdns_mhdp_secure_mailbox_send_recv_multi
> > - MHDP8546 DP and HDCP commands that need access mailbox are
> rewrited
> > with above 6 API functions.
> >
> > v16->v17:
> > - Replaces the local mutex mbox_mutex with a global mutex
> > mhdp_mailbox_mutex
> >
> > v12->v16:
> > *No change.
> >
> > drivers/gpu/drm/bridge/cadence/Kconfig | 4 +
> > drivers/gpu/drm/bridge/cadence/Makefile | 1 +
> > .../gpu/drm/bridge/cadence/cdns-mhdp-helper.c | 414
> +++++++++++++++
> > .../drm/bridge/cadence/cdns-mhdp8546-core.c | 487 +++---------------
> > .../drm/bridge/cadence/cdns-mhdp8546-core.h | 47 +-
> > .../drm/bridge/cadence/cdns-mhdp8546-hdcp.c | 236 +--------
> > .../drm/bridge/cadence/cdns-mhdp8546-hdcp.h | 18 +-
> > include/drm/bridge/cdns-mhdp-helper.h | 130 +++++
> > 8 files changed, 658 insertions(+), 679 deletions(-) create mode
> > 100644 drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> > create mode 100644 include/drm/bridge/cdns-mhdp-helper.h
> >
> > diff --git a/drivers/gpu/drm/bridge/cadence/Kconfig
> > b/drivers/gpu/drm/bridge/cadence/Kconfig
> > index cced81633ddcd..e0973339e9e33 100644
> > --- a/drivers/gpu/drm/bridge/cadence/Kconfig
> > +++ b/drivers/gpu/drm/bridge/cadence/Kconfig
> > @@ -21,6 +21,9 @@ config DRM_CDNS_DSI_J721E
> > the routing of the DSS DPI signal to the Cadence DSI.
> > endif
> >
> > +config CDNS_MHDP_HELPER
> > + tristate
> > +
>
> I'm not sure if the placement for the helper is suitable. Especially if you want
> to reuse the helper by some other subsystem. As far as I don't like it, maybe
> drivers/soc is a better option.
While PHY driver in drivers/phy/freescale also reuse the MHDP helper API,
most of the code reuse happens in drivers/gpu/drm/bridge/cadence.
I think it would be better to keep it in the current location because of this.
>
> > config DRM_CDNS_MHDP8546
> > tristate "Cadence DPI/DP bridge"
> > select DRM_DISPLAY_DP_HELPER
> > @@ -28,6 +31,7 @@ config DRM_CDNS_MHDP8546
> > select DRM_DISPLAY_HELPER
> > select DRM_KMS_HELPER
> > select DRM_PANEL_BRIDGE
> > + select CDNS_MHDP_HELPER
> > depends on OF
> > help
> > Support Cadence DPI to DP bridge. This is an internal diff
> > --git a/drivers/gpu/drm/bridge/cadence/Makefile
> > b/drivers/gpu/drm/bridge/cadence/Makefile
> > index c95fd5b81d137..087dc074820d7 100644
> > --- a/drivers/gpu/drm/bridge/cadence/Makefile
> > +++ b/drivers/gpu/drm/bridge/cadence/Makefile
> > @@ -2,6 +2,7 @@
> > obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o cdns-dsi-y :=
> > cdns-dsi-core.o
> > cdns-dsi-$(CONFIG_DRM_CDNS_DSI_J721E) += cdns-dsi-j721e.o
> > +obj-$(CONFIG_CDNS_MHDP_HELPER) += cdns-mhdp-helper.o
> > obj-$(CONFIG_DRM_CDNS_MHDP8546) += cdns-mhdp8546.o
> cdns-mhdp8546-y
> > := cdns-mhdp8546-core.o cdns-mhdp8546-hdcp.o
> > cdns-mhdp8546-$(CONFIG_DRM_CDNS_MHDP8546_J721E) +=
> > cdns-mhdp8546-j721e.o diff --git
> > a/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> > b/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> > new file mode 100644
> > index 0000000000000..f39228a78c7cb
> > --- /dev/null
> > +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> > @@ -0,0 +1,414 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (C) 2023, 2024 NXP Semiconductor, Inc.
> > + *
> > + */
> > +#include <drm/bridge/cdns-mhdp-helper.h> #include
> > +<linux/dev_printk.h> #include <linux/module.h>
> > +
> > +/* Protects mailbox communications with the firmware */ static
> > +DEFINE_MUTEX(mhdp_mailbox_mutex);
> > +
> > +/* Mailbox helper functions */
> > +static int mhdp_mailbox_read(void __iomem *regs) {
> > + int ret, empty;
> > +
> > + WARN_ON(!mutex_is_locked(&mhdp_mailbox_mutex));
> > +
> > + ret = readx_poll_timeout(readl, regs + CDNS_MAILBOX_EMPTY,
> > + empty, !empty, MAILBOX_RETRY_US,
> > + MAILBOX_TIMEOUT_US);
> > + if (ret < 0)
> > + return ret;
> > +
> > + return readl(regs + CDNS_MAILBOX_RX_DATA) & 0xff; }
> > +
> > +static int mhdp_mailbox_write(void __iomem *regs, u8 val) {
> > + int ret, full;
> > +
> > + WARN_ON(!mutex_is_locked(&mhdp_mailbox_mutex));
> > +
> > + ret = readx_poll_timeout(readl, regs + CDNS_MAILBOX_FULL,
> > + full, !full, MAILBOX_RETRY_US,
> > + MAILBOX_TIMEOUT_US);
> > + if (ret < 0)
> > + return ret;
> > +
> > + writel(val, regs + CDNS_MAILBOX_TX_DATA);
> > +
> > + return 0;
> > +}
> > +
> > +static int mhdp_mailbox_recv_header(void __iomem *regs,
> > + u8 module_id, u8 opcode,
> > + u16 req_size) {
> > + u32 mbox_size, i;
> > + u8 header[4];
> > + int ret;
> > +
> > + /* read the header of the message */
> > + for (i = 0; i < sizeof(header); i++) {
> > + ret = mhdp_mailbox_read(regs);
> > + if (ret < 0)
> > + return ret;
> > +
> > + header[i] = ret;
> > + }
> > +
> > + mbox_size = get_unaligned_be16(header + 2);
> > +
> > + if (opcode != header[0] || module_id != header[1] ||
> > + (opcode != HDCP_TRAN_IS_REC_ID_VALID && req_size !=
> > + mbox_size)) {
>
> Could you please explain the second clause?
This is a special case where the number of data received is not fixed.
It needs to be parsed from the previous data, but there is a maximum limit.
I will comment it.
>
> > + /*
> > + * If the message in mailbox is not what we want, we
> need to
> > + * clear the mailbox by reading its contents.
> > + */
> > + for (i = 0; i < mbox_size; i++)
> > + if (mhdp_mailbox_read(regs) < 0)
> > + break;
> > +
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int mhdp_mailbox_recv_data(void __iomem *regs,
> > + u8 *buff, u16 buff_size) {
> > + u32 i;
> > + int ret;
> > +
> > + for (i = 0; i < buff_size; i++) {
> > + ret = mhdp_mailbox_read(regs);
> > + if (ret < 0)
> > + return ret;
> > +
> > + buff[i] = ret;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int mhdp_mailbox_send(void __iomem *regs, u8 module_id,
> > + u8 opcode, u16 size, u8 *message) {
> > + u8 header[4];
> > + int ret, i;
> > +
> > + header[0] = opcode;
> > + header[1] = module_id;
> > + put_unaligned_be16(size, header + 2);
> > +
> > + for (i = 0; i < sizeof(header); i++) {
> > + ret = mhdp_mailbox_write(regs, header[i]);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + for (i = 0; i < size; i++) {
> > + ret = mhdp_mailbox_write(regs, message[i]);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + return 0;
> > +}
> > +
>
> Please add kerneldocs for all new API. It's obvious for the simple ones, but not
> for the more complex functions.
OK, I will add them.
>
> > +int cdns_mhdp_mailbox_send(struct cdns_mhdp_base *base, u8
> module_id,
> > + u8 opcode, u16 size, u8 *message) {
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
>
> guard(mutex)(&mhdp_mailbox_mutex);
>
> return mhdp_mailbox_send(...);
>
> Similar changes can be applied further on.
OK.
>
> > +
> > + ret = mhdp_mailbox_send(base->regs, module_id, opcode, size,
> > + message);
> > +
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_mailbox_send);
> > +
> > +int cdns_mhdp_mailbox_send_recv(struct cdns_mhdp_base *base,
> > + u8 module_id, u8 opcode,
> > + u16 msg_size, u8 *msg,
> > + u16 resp_size, u8 *resp) {
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
> > +
> > + ret = mhdp_mailbox_send(base->regs, module_id,
> > + opcode, msg_size, msg);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_header(base->regs, module_id,
> > + opcode, resp_size);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_data(base->regs, resp, resp_size);
> > +out:
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + if (ret)
> > + dev_err(base->dev, "ModuleID=%d, CMD=%d
> failed: %d\n",
> > + module_id, opcode, ret);
>
> Using guard() would allow you to use precise messages, e.g. failed to send,
> failed to received header, failed to receive data.
Yes, more precise messages will be added.
>
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_mailbox_send_recv);
> > +
>
> Like what is _multi? Why do you need to fetch into two separate buffers?
> Can you fetch into one and then parse it accordingly? Please don't make the
> API more complicated than necessary.
>
The majority of mailbox access commands can be implemented using the function cdns_mhdp_mailbox_send_recv()
because the length of the response data is fixed based on the response type.
However, there are three types of exceptions:
Read operations: DPTX's DPTX_READ_DPCD and HDMITX's HDMI_TX_READ have variable response data lengths that depend on the caller's requirements.
HDCPTX's HDCP_TRAN_IS_REC_ID_VALID: The response data length varies based on the type of connected HDCP receivers.
Therefore, it's necessary to read a portion of the response data first, parse it, and then read the entire content.
MHDP8546 link training DPTX_ADJUST_LT: The opcode for sending the message differs from the opcode for receiving the response.
Considering these special cases,
two new functions, cdns_mhdp_mailbox_send_recv_multi() and cdns_mhdp_secure_mailbox_send_recv_multi(),
have been created to handle these specific scenarios.
> > +int cdns_mhdp_mailbox_send_recv_multi(struct cdns_mhdp_base *base,
> > + u8 module_id, u8 opcode,
> > + u16 msg_size, u8 *msg,
> > + u8 opcode_resp,
> > + u16 resp1_size, u8 *resp1,
> > + u16 resp2_size, u8 *resp2) {
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
> > +
> > + ret = mhdp_mailbox_send(base->regs, module_id,
> > + opcode, msg_size, msg);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_header(base->regs, module_id,
> opcode_resp,
> > + resp1_size + resp2_size);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_data(base->regs, resp1, resp1_size);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_data(base->regs, resp2, resp2_size);
> > +out:
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + if (ret)
> > + dev_err(base->dev, "ModuleID=%d, MSG_CMD=%d
> Resp_CMD=%d failed: %d\n",
> > + module_id, opcode, opcode_resp, ret);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_mailbox_send_recv_multi);
> > +
> > +/*
> > + * Secure mailbox access functions:
> > + * These functions handle secure mailbox communication, which differs
> > + * from non-secure mailbox access. They use the secure address.
> > + */
> > +int cdns_mhdp_secure_mailbox_send(struct cdns_mhdp_base *base, u8
> module_id,
> > + u8 opcode, u16 size, u8 *message) {
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
> > +
> > + ret = mhdp_mailbox_send(base->sapb_regs, module_id, opcode,
> > + size, message);
> > +
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_secure_mailbox_send);
> > +
> > +int cdns_mhdp_secure_mailbox_send_recv(struct cdns_mhdp_base
> *base,
> > + u8 module_id, u8 opcode,
> > + u16 msg_size, u8 *msg,
> > + u16 resp_size, u8 *resp) {
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
> > +
> > + ret = mhdp_mailbox_send(base->sapb_regs, module_id,
> > + opcode, msg_size, msg);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_header(base->sapb_regs, module_id,
> > + opcode, resp_size);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_data(base->sapb_regs, resp, resp_size);
> > +out:
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + if (ret)
> > + dev_err(base->dev, "ModuleID=%d, CMD=%d
> failed: %d\n",
> > + module_id, opcode, ret);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_secure_mailbox_send_recv);
> > +
> > +int cdns_mhdp_secure_mailbox_send_recv_multi(struct cdns_mhdp_base
> *base,
> > + u8 module_id, u8
> opcode,
> > + u16 msg_size, u8
> *msg,
> > + u8 opcode_resp,
> > + u16 resp1_size, u8
> *resp1,
> > + u16 resp2_size, u8
> *resp2)
> > +{
> > + int ret;
> > +
> > + mutex_lock(&mhdp_mailbox_mutex);
> > +
> > + ret = mhdp_mailbox_send(base->sapb_regs, module_id,
> > + opcode, msg_size, msg);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_header(base->sapb_regs, module_id,
> > + opcode_resp,
> > + resp1_size + resp2_size);
> > + if (ret)
> > + goto out;
> > +
> > + ret = mhdp_mailbox_recv_data(base->sapb_regs, resp1,
> resp1_size);
> > + if (ret)
> > + goto out;
> > +
> > + if (module_id == MB_MODULE_ID_HDCP_TX &&
> > + opcode == HDCP_TRAN_IS_REC_ID_VALID)
>
> comment, please.
OK.
>
> > + ret = mhdp_mailbox_recv_data(base->sapb_regs, resp2, 5
> * resp1[0]);
> > + else
> > + ret = mhdp_mailbox_recv_data(base->sapb_regs, resp2,
> > +resp2_size);
> > +out:
> > + mutex_unlock(&mhdp_mailbox_mutex);
> > +
> > + if (ret)
> > + dev_err(base->dev, "ModuleID=%d, CMD=%d
> failed: %d\n",
> > + module_id, opcode, ret);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_secure_mailbox_send_recv_multi);
> > +
> > +/* General read/write helper functions */ int
> > +cdns_mhdp_reg_read(struct cdns_mhdp_base *base, u32 addr, u32
> *value)
> > +{
> > + u8 msg[4], resp[8];
> > + int ret;
> > +
> > + put_unaligned_be32(addr, msg);
> > +
> > + ret = cdns_mhdp_mailbox_send_recv(base,
> MB_MODULE_ID_GENERAL,
> > +
> GENERAL_REGISTER_READ,
> > + sizeof(msg), msg,
> sizeof(resp), resp);
> > + if (ret)
> > + goto out;
> > +
> > + /* Returned address value should be the same as requested */
> > + if (memcmp(msg, resp, sizeof(msg))) {
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > +
> > + *value = get_unaligned_be32(resp + 4);
> > +out:
> > + if (ret) {
> > + dev_err(base->dev, "Failed to read register\n");
> > + *value = 0;
> > + }
> > +
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_reg_read);
> > +
> > +int cdns_mhdp_reg_write(struct cdns_mhdp_base *base, u32 addr, u32
> > +val) {
> > + u8 msg[8];
> > +
> > + put_unaligned_be32(addr, msg);
> > + put_unaligned_be32(val, msg + 4);
> > +
> > + return cdns_mhdp_mailbox_send(base,
> MB_MODULE_ID_GENERAL,
> > + GENERAL_REGISTER_WRITE,
> > + sizeof(msg), msg); }
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_reg_write);
> > +
> > +/* DPTX helper functions */
> > +int cdns_mhdp_dp_reg_write(struct cdns_mhdp_base *base, u16 addr,
> u32
> > +val) {
> > + u8 msg[6];
> > +
> > + put_unaligned_be16(addr, msg);
> > + put_unaligned_be32(val, msg + 2);
> > +
> > + return cdns_mhdp_mailbox_send(base, MB_MODULE_ID_DP_TX,
> > + DPTX_WRITE_REGISTER,
> sizeof(msg),
> > +msg); } EXPORT_SYMBOL_GPL(cdns_mhdp_dp_reg_write);
>
> Please don't add API without a user. If the function is required in the following
> patch, add it there.
OK, cdns_mhdp_dp_reg_write() will be removed.
B.R
Sandor
>
> > +
> > +int cdns_mhdp_dp_reg_write_bit(struct cdns_mhdp_base *base, u16 addr,
> > + u8 start_bit, u8 bits_no, u32 val) {
> > + u8 field[8];
> > +
> > + put_unaligned_be16(addr, field);
> > + field[2] = start_bit;
> > + field[3] = bits_no;
> > + put_unaligned_be32(val, field + 4);
> > +
> > + return cdns_mhdp_mailbox_send(base, MB_MODULE_ID_DP_TX,
> > + DPTX_WRITE_FIELD,
> sizeof(field),
> > +field); } EXPORT_SYMBOL_GPL(cdns_mhdp_dp_reg_write_bit);
> > +
> > +int cdns_mhdp_dpcd_read(struct cdns_mhdp_base *base,
> > + u32 addr, u8 *data, u16 len) {
> > + u8 msg[5], reg[5];
> > +
> > + put_unaligned_be16(len, msg);
> > + put_unaligned_be24(addr, msg + 2);
> > +
> > + return cdns_mhdp_mailbox_send_recv_multi(base,
> > +
> MB_MODULE_ID_DP_TX,
> > +
> DPTX_READ_DPCD,
> > + sizeof(msg), msg,
> > +
> DPTX_READ_DPCD,
> > + sizeof(reg), reg,
> > + len, data); }
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_dpcd_read);
> > +
> > +int cdns_mhdp_dpcd_write(struct cdns_mhdp_base *base, u32 addr, u8
> > +value) {
> > + u8 msg[6], reg[5];
> > + int ret;
> > +
> > + put_unaligned_be16(1, msg);
> > + put_unaligned_be24(addr, msg + 2);
> > + msg[5] = value;
> > +
> > + ret = cdns_mhdp_mailbox_send_recv(base,
> MB_MODULE_ID_DP_TX,
> > + DPTX_WRITE_DPCD,
> > + sizeof(msg), msg,
> sizeof(reg), reg);
> > + if (ret) {
> > + dev_err(base->dev, "dpcd write failed: %d\n", ret);
> > + return ret;
> > + }
> > +
> > + if (addr != get_unaligned_be24(reg + 2)) {
> > + dev_err(base->dev, "Invalid response: expected address
> 0x%06x, got 0x%06x\n",
> > + addr, get_unaligned_be24(reg + 2));
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(cdns_mhdp_dpcd_write);
> > +
> > +MODULE_DESCRIPTION("Cadence MHDP Helper driver");
> > +MODULE_AUTHOR("Sandor Yu <Sandor.yu@....com>");
> > +MODULE_LICENSE("GPL");
>
> --
> With best wishes
> Dmitry
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