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Date:   Mon, 20 Jun 2022 14:28:25 +0700
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From:   Quan Nguyen <quan@os.amperecomputing.com>
Subject: Re: [PATCH v8 1/3] ipmi: ssif_bmc: Add SSIF BMC driver
To:     Ryan Chen <ryan_chen@aspeedtech.com>,
        Corey Minyard <minyard@acm.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Brendan Higgins <brendanhiggins@google.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Joel Stanley <joel@jms.id.au>,
        Andrew Jeffery <andrew@aj.id.au>,
        Wolfram Sang <wsa@kernel.org>,
        "openipmi-developer@lists.sourceforge.net" 
        <openipmi-developer@lists.sourceforge.net>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
        "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>
Cc:     Open Source Submission <patches@amperecomputing.com>,
        "Thang Q . Nguyen" <thang@os.amperecomputing.com>,
        Phong Vo <phong@os.amperecomputing.com>
References: <20220615090259.1121405-1-quan@os.amperecomputing.com>
 <20220615090259.1121405-2-quan@os.amperecomputing.com>
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On 16/06/2022 17:47, Ryan Chen wrote:
> Hello Nquyen,
> 
>> -----Original Message-----
>> From: Linux-aspeed
>> <linux-aspeed-bounces+ryan_chen=aspeedtech.com@lists.ozlabs.org> On
>> Behalf Of Quan Nguyen
>> Sent: Wednesday, June 15, 2022 5:03 PM
>> To: Quan Nguyen <quan@os.amperecomputing.com>; Corey Minyard
>> <minyard@acm.org>; Rob Herring <robh+dt@kernel.org>; Krzysztof Kozlowski
>> <krzysztof.kozlowski+dt@linaro.org>; Brendan Higgins
>> <brendanhiggins@google.com>; Benjamin Herrenschmidt
>> <benh@kernel.crashing.org>; Joel Stanley <joel@jms.id.au>; Andrew Jeffery
>> <andrew@aj.id.au>; Wolfram Sang <wsa@kernel.org>;
>> openipmi-developer@lists.sourceforge.net; devicetree@vger.kernel.org;
>> linux-kernel@vger.kernel.org; linux-i2c@vger.kernel.org;
>> openbmc@lists.ozlabs.org; linux-arm-kernel@lists.infradead.org;
>> linux-aspeed@lists.ozlabs.org
>> Cc: Open Source Submission <patches@amperecomputing.com>; Thang Q .
>> Nguyen <thang@os.amperecomputing.com>; Phong Vo
>> <phong@os.amperecomputing.com>
>> Subject: [PATCH v8 1/3] ipmi: ssif_bmc: Add SSIF BMC driver
>>
>> The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
>> in-band IPMI communication with their host in management (BMC) side.
>>
>> Thanks Dan for the copy_from_user() fix in the link below.
>>
>> Link:
>> https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.a
>> mperecomputing.com/
>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
>> ---
>> v8:
>>    + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   [Corey]
>>    + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
>>    header file
>> [Corey]
>>    + Use unsigned int for len field in struct ipmi_ssif_msg       [Corey]
>>    + Avoid using packed structure
>> [Corey]
>>    + Add comment to clarify the logic flow                        [Corey]
>>    + Fix multipart read end with len=0 issue                      [Corey]
>>    + Refactor code handle the too big request message             [Corey]
>>    + Fix code indentation issue
>> [Corey]
>>    + Clean buffer before receiving request to avoid garbage        [Quan]
>>    + Fix the license to SPDX-License-Identifier: GPL-2.0-only      [Quan]
>>
>> v7:
>>    + Remove unneccessary del_timer() in response_timeout()        [Corey]
>>    + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  [Jae]
>>    + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    [Jae]
>>    + Dropped the use of ssif_msg_len() macro, use the len directly [Quan]
>>    + Solve possible issue if both response timer and ssif_bmc_write()
>>    occurred at the same time
>> [Corey]
>>    + Fix wrong return type of ssif_bmc_poll()         [kernel robot test]
>>    + Refactor and introduce ssif_part_buffer struct to replace the
>>    response_buf to manage each send/receive part of ssif           [Quan]
>>    + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state
>> [Corey]
>>    + Support abort feature to skip the current bad request/response and
>>    wait until next new request
>> [Corey]
>>    + Refactor the PEC calculation to avoid the re-calculate the PEC on
>>    each I2C_SLAVE_WRITE_RECEIVED event
>> [Quan]
>>    + Fix the use of error-proned idx                              [Corey]
>>    + Defer the test for valid SMBus command until the read/write part
>>    is determined
>> [Quan]
>>    + Change/split unsupported_smbus_cmd() to
>>    supported_[write|read]_cmd()
>> [Corey]
>>    + Abort the request if somehow its size exceeded 255 bytes      [Quan]
>>
>> v6:
>>    + Drop the use of slave_enable()
>> [Wolfram]
>>    + Make i2c-aspeed to issue RxCmdLast command on all
>>    I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy
>> [Quan]
>>    + Make i2c slave to return -EBUSY when it's busy                [Quan]
>>    + Drop the aborting feature as return Completion Code 0xFF may stop
>>    host to retry and make ipmi_ssif.so fails to load               [Quan]
>>    + Add timer to recover slave from busy state when no response   [Quan]
>>    + Clean request/response buffer appropriately                   [Quan]
>>    + Add some minor change on error and warning messages
>> [Quan]
>>
>> v5:
>>    + None
>>
>> v4:
>>    + Send response with Completion code 0xFF when aborting
>> [Quan]
>>    + Added bounding check on SMBus writes and the whole request     [Dan]
>>    + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>>      corruption if somehow buffer is written past the end           [Dan]
>>    + Return -EINVAL if userspace buffer too small, dont
>>      silence truncate                                       [Corey,
>> Joel]
>>    + Not necessary to check NONBLOCK in lock
>> [Corey]
>>    + Enforce one user at a time
>> [Joel]
>>    + Reject write with invalid response length from userspace     [Corey]
>>    + Add state machines for better ssif bmc state handling         [Quan]
>>    + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>>      SSIF BMC driver
>> [Quan]
>>    + Change compatible string "aspeed,ast2500-ssif-bmc" to
>>      "ampere,ssif-bmc"
>> [Quan]
>>    + Abort current request with invalid SMBus write or
>>      invalid command
>> [Quan]
>>    + Abort all request if there is pending response                [Quan]
>>    + Changed validate_pec() to validate_request()                  [Quan]
>>    + Add unsupported_smbus_cmd() to handle unknown SMBus command
>> [Quan]
>>    + Print internal state string for ease investigating issue      [Quan]
>>    + Move to READY state on SLAVE_STOP event
>> [Quan]
>>    + Change initilize_transfer() to process_smbus_cmd()            [Quan]
>>    + Introduce functions for each slave event                      [Quan]
>>
>> v3:
>>    + Removed redundant license info
>> [Joel]
>>    + Switched to use traditional if-else                           [Joel]
>>    + Removed unused ssif_bmc_ioctl()
>> [Joel]
>>    + Made handle_request()/complete_response() to return void      [Joel]
>>    + Refactored send_ssif_bmc_response() and
>>    receive_ssif_bmc_request()
>> [Corey]
>>    + Removed mutex
>> [Corey]
>>    + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
>>    + Removed the unnecessary memset
>> [Corey]
>>    + Switch to use dev_err()
>> [Corey]
>>
>> v2:
>>    + Fixed compiling error with COMPILE_TEST for arc
>>
>>   drivers/char/ipmi/Kconfig          |  11 +
>>   drivers/char/ipmi/Makefile         |   1 +
>>   drivers/char/ipmi/ssif_bmc.c       | 880
>> +++++++++++++++++++++++++++++
>>   include/uapi/linux/ipmi_ssif_bmc.h |  16 +
>>   4 files changed, 908 insertions(+)
>>   create mode 100644 drivers/char/ipmi/ssif_bmc.c  create mode 100644
>> include/uapi/linux/ipmi_ssif_bmc.h
>>
>> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig index
>> b061e6b513ed..18a89093d64e 100644
>> --- a/drivers/char/ipmi/Kconfig
>> +++ b/drivers/char/ipmi/Kconfig
>> @@ -169,6 +169,17 @@ config ASPEED_BT_IPMI_BMC
>>   	  found on Aspeed SOCs (AST2400 and AST2500). The driver
>>   	  implements the BMC side of the BT interface.
>>
>> +config SSIF_IPMI_BMC
>> +	tristate "SSIF IPMI BMC driver"
>> +	select I2C
>> +	select I2C_SLAVE
>> +	help
>> +	  This enables the IPMI SMBus system interface (SSIF) at the
>> +	  management (BMC) side.
>> +
>> +	  The driver implements the BMC side of the SMBus system
>> +	  interface (SSIF).
>> +
>>   config IPMB_DEVICE_INTERFACE
>>   	tristate 'IPMB Interface handler'
>>   	depends on I2C
>> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile index
>> 7ce790efad92..cb6138b8ded9 100644
>> --- a/drivers/char/ipmi/Makefile
>> +++ b/drivers/char/ipmi/Makefile
>> @@ -30,3 +30,4 @@ obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
>>   obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
>>   obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
>>   obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o
>> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
>> diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c new
>> file mode 100644 index 000000000000..0bfd4b9bbaf1
>> --- /dev/null
>> +++ b/drivers/char/ipmi/ssif_bmc.c
>> @@ -0,0 +1,880 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * The driver for BMC side of SSIF interface
>> + *
>> + * Copyright (c) 2022, Ampere Computing LLC
>> + *
>> + */
>> +
>> +#include <linux/i2c.h>
>> +#include <linux/miscdevice.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/poll.h>
>> +#include <linux/sched.h>
>> +#include <linux/mutex.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/timer.h>
>> +#include <linux/jiffies.h>
>> +#include <linux/ipmi_ssif_bmc.h>
>> +
>> +#define DEVICE_NAME                             "ipmi-ssif-host"
>> +
>> +#define GET_8BIT_ADDR(addr_7bit)                (((addr_7bit) << 1) &
>> 0xff)
>> +
>> +/* A standard SMBus Transaction is limited to 32 data bytes */
>> +#define MAX_PAYLOAD_PER_TRANSACTION             32
>> +/* Transaction includes the address, the command, the length and the PEC
>> byte */
>> +#define MAX_TRANSACTION
>> (MAX_PAYLOAD_PER_TRANSACTION + 4)
>> +
>> +#define MAX_IPMI_DATA_PER_START_TRANSACTION     30
>> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION    31
>> +
>> +#define SSIF_IPMI_SINGLEPART_WRITE              0x2
>> +#define SSIF_IPMI_SINGLEPART_READ               0x3
>> +#define SSIF_IPMI_MULTIPART_WRITE_START         0x6
>> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE        0x7
>> +#define SSIF_IPMI_MULTIPART_WRITE_END           0x8
>> +#define SSIF_IPMI_MULTIPART_READ_START          0x3
>> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE         0x9
>> +
>> +/*
>> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
>> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
>> + * Recover ssif_bmc from busy state if it takes up to 500ms  */
>> +#define RESPONSE_TIMEOUT                        500 /* ms */
>> +
>> +struct ssif_part_buffer {
>> +	u8 address;
>> +	u8 smbus_cmd;
>> +	u8 length;
>> +	u8 payload[MAX_PAYLOAD_PER_TRANSACTION];
>> +	u8 pec;
>> +	u8 index;
>> +};
>> +
>> +/*
>> + * SSIF internal states:
>> + *   SSIF_READY         0x00 : Ready state
>> + *   SSIF_START         0x01 : Start smbus transaction
>> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
>> + *   SSIF_REQ_RECVING   0x03 : Receiving request
>> + *   SSIF_RES_SENDING   0x04 : Sending response
>> + *   SSIF_BAD_SMBUS     0x05 : Bad SMbus transaction
>> + */
>> +enum ssif_state {
>> +	SSIF_READY,
>> +	SSIF_START,
>> +	SSIF_SMBUS_CMD,
>> +	SSIF_REQ_RECVING,
>> +	SSIF_RES_SENDING,
>> +	SSIF_ABORTING,
>> +	SSIF_STATE_MAX
>> +};
>> +
>> +struct ssif_bmc_ctx {
>> +	struct i2c_client       *client;
>> +	struct miscdevice       miscdev;
>> +	int                     msg_idx;
>> +	bool                    pec_support;
>> +	/* ssif bmc spinlock */
>> +	spinlock_t              lock;
>> +	wait_queue_head_t       wait_queue;
>> +	u8                      running;
>> +	enum ssif_state         state;
>> +	/* Timeout waiting for response */
>> +	struct timer_list       response_timer;
>> +	bool                    response_timer_inited;
>> +	/* Flag to identify a Multi-part Read Transaction */
>> +	bool                    is_singlepart_read;
>> +	u8                      nbytes_processed;
>> +	u8                      remain_len;
>> +	u8                      recv_len;
>> +	/* Block Number of a Multi-part Read Transaction */
>> +	u8                      block_num;
>> +	bool                    request_available;
>> +	bool                    response_in_progress;
>> +	bool                    busy;
>> +	bool                    aborting;
>> +	/* Buffer for SSIF Transaction part*/
>> +	struct ssif_part_buffer part_buf;
>> +	struct ipmi_ssif_msg    response;
>> +	struct ipmi_ssif_msg    request;
>> +};
>> +
>> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file) {
>> +	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
>> +}
>> +
>> +static const char *state_to_string(enum ssif_state state) {
>> +	switch (state) {
>> +	case SSIF_READY:
>> +		return "SSIF_READY";
>> +	case SSIF_START:
>> +		return "SSIF_START";
>> +	case SSIF_SMBUS_CMD:
>> +		return "SSIF_SMBUS_CMD";
>> +	case SSIF_REQ_RECVING:
>> +		return "SSIF_REQ_RECVING";
>> +	case SSIF_RES_SENDING:
>> +		return "SSIF_RES_SENDING";
>> +	case SSIF_ABORTING:
>> +		return "SSIF_ABORTING";
>> +	default:
>> +		return "SSIF_STATE_UNKNOWN";
>> +	}
>> +}
>> +
>> +/* Handle SSIF message that will be sent to user */ static ssize_t
>> +ssif_bmc_read(struct file *file, char __user *buf, size_t count, loff_t
>> +*ppos) {
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	struct ipmi_ssif_msg msg;
>> +	unsigned long flags;
>> +	ssize_t ret;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	while (!ssif_bmc->request_available) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		if (file->f_flags & O_NONBLOCK)
>> +			return -EAGAIN;
>> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +					       ssif_bmc->request_available);
>> +		if (ret)
>> +			return ret;
>> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	}
>> +
>> +	if (count < min_t(ssize_t,
>> +			  sizeof_field(struct ipmi_ssif_msg, len) +
>> ssif_bmc->request.len,
>> +			  sizeof(struct ipmi_ssif_msg))) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		ret = -EINVAL;
>> +	} else {
>> +		count = min_t(ssize_t,
>> +			      sizeof_field(struct ipmi_ssif_msg, len) +
>> ssif_bmc->request.len,
>> +			      sizeof(struct ipmi_ssif_msg));
>> +		memcpy(&msg, &ssif_bmc->request, count);
>> +		ssif_bmc->request_available = false;
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +		ret = copy_to_user(buf, &msg, count);
>> +	}
>> +
>> +	return (ret < 0) ? ret : count;
>> +}
>> +
>> +/* Handle SSIF message that is written by user */ static ssize_t
>> +ssif_bmc_write(struct file *file, const char __user *buf, size_t count,
>> +			      loff_t *ppos)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	struct ipmi_ssif_msg msg;
>> +	unsigned long flags;
>> +	ssize_t ret;
>> +
>> +	if (count > sizeof(struct ipmi_ssif_msg))
>> +		return -EINVAL;
>> +
>> +	if (copy_from_user(&msg, buf, count))
>> +		return -EFAULT;
>> +
>> +	if (!msg.len || count < sizeof_field(struct ipmi_ssif_msg, len) + msg.len)
>> +		return -EINVAL;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	while (ssif_bmc->response_in_progress) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		if (file->f_flags & O_NONBLOCK)
>> +			return -EAGAIN;
>> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +					       !ssif_bmc->response_in_progress);
>> +		if (ret)
>> +			return ret;
>> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	}
>> +
>> +	/*
>> +	 * The write must complete before the response timeout fired, otherwise
>> +	 * the response is aborted and wait for next request
>> +	 * Return -EINVAL if the response is aborted
>> +	 */
>> +	ret = (ssif_bmc->response_timer_inited) ? 0 : -EINVAL;
>> +	if (ret)
>> +		goto exit;
>> +
>> +	del_timer(&ssif_bmc->response_timer);
>> +	ssif_bmc->response_timer_inited = false;
>> +
>> +	memcpy(&ssif_bmc->response, &msg, count);
>> +	ssif_bmc->is_singlepart_read = (msg.len <=
>> +MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +	ssif_bmc->response_in_progress = true;
>> +
>> +	/* ssif_bmc not busy */
>> +	ssif_bmc->busy = false;
>> +
>> +	/* Clean old request buffer */
>> +	memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
>> +exit:
>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +	return (ret < 0) ? ret : count;
>> +}
>> +
>> +static int ssif_bmc_open(struct inode *inode, struct file *file) {
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	int ret = 0;
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	if (!ssif_bmc->running)
>> +		ssif_bmc->running = 1;
>> +	else
>> +		ret = -EBUSY;
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return ret;
>> +}
>> +
>> +static __poll_t ssif_bmc_poll(struct file *file, poll_table *wait) {
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	__poll_t mask = 0;
>> +
>> +	poll_wait(file, &ssif_bmc->wait_queue, wait);
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	/* The request is available, userspace application can get the request */
>> +	if (ssif_bmc->request_available)
>> +		mask |= POLLIN;
>> +
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return mask;
>> +}
>> +
>> +static int ssif_bmc_release(struct inode *inode, struct file *file) {
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	ssif_bmc->running = 0;
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * System calls to device interface for user apps  */ static const
>> +struct file_operations ssif_bmc_fops = {
>> +	.owner		= THIS_MODULE,
>> +	.open		= ssif_bmc_open,
>> +	.read		= ssif_bmc_read,
>> +	.write		= ssif_bmc_write,
>> +	.release	= ssif_bmc_release,
>> +	.poll		= ssif_bmc_poll,
>> +};
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc) {
>> +	/* Invalidate response in buffer to denote it having been sent. */
>> +	ssif_bmc->response.len = 0;
>> +	ssif_bmc->response_in_progress = false;
>> +	ssif_bmc->nbytes_processed = 0;
>> +	ssif_bmc->remain_len = 0;
>> +	ssif_bmc->busy = false;
>> +	memset(&ssif_bmc->part_buf, 0, sizeof(struct ssif_part_buffer));
>> +	wake_up_all(&ssif_bmc->wait_queue);
>> +}
>> +
>> +static void response_timeout(struct timer_list *t) {
>> +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +
>> +	/* Do nothing if the response is in progress */
>> +	if (!ssif_bmc->response_in_progress) {
>> +		/* Recover ssif_bmc from busy */
>> +		ssif_bmc->busy = false;
>> +		ssif_bmc->response_timer_inited = false;
>> +		/* Set aborting flag */
>> +		ssif_bmc->aborting = true;
>> +	}
>> +
>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags); }
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc) {
>> +	/* set ssif_bmc to busy waiting for response */
>> +	ssif_bmc->busy = true;
>> +	/* Request message is available to process */
>> +	ssif_bmc->request_available = true;
>> +	/* Clean old response buffer */
>> +	memset(&ssif_bmc->response, 0, sizeof(struct ipmi_ssif_msg));
>> +	/* This is the new READ request.*/
>> +	wake_up_all(&ssif_bmc->wait_queue);
>> +
>> +	/* Armed timer to recover slave from busy state in case of no response */
>> +	if (!ssif_bmc->response_timer_inited) {
>> +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
>> +		ssif_bmc->response_timer_inited = true;
>> +	}
>> +	mod_timer(&ssif_bmc->response_timer, jiffies +
>> +msecs_to_jiffies(RESPONSE_TIMEOUT));
>> +}
>> +
>> +static void calculate_response_part_pec(struct ssif_part_buffer *part)
>> +{
>> +	u8 addr = part->address;
>> +
>> +	/* PEC - Start Read Address */
>> +	part->pec = i2c_smbus_pec(0, &addr, 1);
>> +	/* PEC - SSIF Command */
>> +	part->pec = i2c_smbus_pec(part->pec, &part->smbus_cmd, 1);
>> +	/* PEC - Restart Write Address */
>> +	addr = addr | 0x01;
>> +	part->pec = i2c_smbus_pec(part->pec, &addr, 1);
>> +	part->pec = i2c_smbus_pec(part->pec, &part->length, 1);
>> +	if (part->length)
>> +		part->pec = i2c_smbus_pec(part->pec, part->payload,
>> part->length); }
>> +
>> +static void set_singlepart_response_buffer(struct ssif_bmc_ctx
>> +*ssif_bmc) {
>> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +	part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +	part->length = (u8)ssif_bmc->response.len;
>> +
>> +	/* Clear the rest to 0 */
>> +	memset(part->payload + part->length, 0,
>> MAX_PAYLOAD_PER_TRANSACTION - part->length);
>> +	memcpy(&part->payload[0], &ssif_bmc->response.payload[0],
>> +part->length); }
>> +
>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx
>> +*ssif_bmc) {
>> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +	u8 part_len = 0;
>> +
>> +	part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +	switch (part->smbus_cmd) {
>> +	case SSIF_IPMI_MULTIPART_READ_START:
>> +		/*
>> +		 * Read Start length is 32 bytes.
>> +		 * Read Start transfer first 30 bytes of IPMI response
>> +		 * and 2 special code 0x00, 0x01.
>> +		 */
>> +		ssif_bmc->nbytes_processed = 0;
>> +		ssif_bmc->block_num = 0;
>> +		part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +		part_len = MAX_IPMI_DATA_PER_START_TRANSACTION;
>> +		ssif_bmc->remain_len = ssif_bmc->response.len - part_len;
>> +
>> +		part->payload[0] = 0x00; /* Start Flag */
>> +		part->payload[1] = 0x01; /* Start Flag */
>> +
>> +		memcpy(&part->payload[2], &ssif_bmc->response.payload[0],
>> part_len);
>> +		break;
>> +
>> +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>> +		/*
>> +		 * IPMI READ Middle or READ End messages can carry up to 31
>> bytes
>> +		 * IPMI data plus block number byte.
>> +		 */
>> +		if (ssif_bmc->remain_len <=
>> MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
>> +			/*
>> +			 * This is READ End message
>> +			 *  Return length is the remaining response data length
>> +			 *  plus block number
>> +			 *  Block number 0xFF is to indicate this is last message
>> +			 *
>> +			 */
>> +			/* Clean the buffer */
>> +			memset(&part->payload[0], 0,
>> MAX_PAYLOAD_PER_TRANSACTION);
>> +			part->length = ssif_bmc->remain_len + 1;
>> +			part_len = ssif_bmc->remain_len;
>> +			ssif_bmc->block_num = 0xFF;
>> +			part->payload[0] = ssif_bmc->block_num;
>> +		} else {
>> +			/*
>> +			 * This is READ Middle message
>> +			 *  Response length is the maximum SMBUS transfer length
>> +			 *  Block number byte is incremented
>> +			 * Return length is maximum SMBUS transfer length
>> +			 */
>> +			part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +			part_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>> +			part->payload[0] = ssif_bmc->block_num;
>> +			ssif_bmc->block_num++;
>> +		}
>> +
>> +		ssif_bmc->remain_len -= part_len;
>> +		memcpy(&part->payload[1], ssif_bmc->response.payload +
>> ssif_bmc->nbytes_processed,
>> +		       part_len);
>> +		break;
>> +
>> +	default:
>> +		/* Do not expect to go to this case */
>> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command
>> 0x%x\n",
>> +			__func__, part->smbus_cmd);
>> +		break;
>> +	}
>> +
>> +	ssif_bmc->nbytes_processed += part_len; }
>> +
>> +static bool supported_read_cmd(u8 cmd)
>> +{
>> +	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
>> +	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
>> +	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> +static bool supported_write_cmd(u8 cmd) {
>> +	if (cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_END)
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>> +/* Process the IPMI response that will be read by master */ static void
>> +handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val) {
>> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +	/* msg_idx start from 0 */
>> +	if (part->index < part->length)
>> +		*val = part->payload[part->index];
>> +	else if (part->index == part->length && ssif_bmc->pec_support)
>> +		*val = part->pec;
>> +	else
>> +		*val = 0;
>> +
>> +	part->index++;
>> +}
>> +
>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8
>> +*val) {
>> +	/*
>> +	 * The msg_idx must be 1 when first enter SSIF_REQ_RECVING state
>> +	 * And it would never exceeded 36 bytes included the 32 bytes max
>> payload +
>> +	 * the address + the command + the len and the PEC.
>> +	 */
>> +	if (ssif_bmc->msg_idx < 1  || ssif_bmc->msg_idx > MAX_TRANSACTION)
>> +		return;
>> +
>> +	if (ssif_bmc->msg_idx == 1) {
>> +		ssif_bmc->part_buf.length = *val;
>> +		ssif_bmc->part_buf.index = 0;
>> +	} else {
>> +		ssif_bmc->part_buf.payload[ssif_bmc->part_buf.index++] = *val;
>> +	}
>> +
>> +	ssif_bmc->msg_idx++;
>> +}
>> +
>> +static bool validate_request_part(struct ssif_bmc_ctx *ssif_bmc) {
>> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +	bool ret = true;
>> +	u8 cpec;
>> +	u8 addr;
>> +
>> +	if (part->index == part->length) {
>> +		/* PEC is not included */
>> +		ssif_bmc->pec_support = false;
>> +		ret = true;
>> +		goto exit;
>> +	}
>> +
>> +	if (part->index != part->length + 1) {
>> +		ret = false;
>> +		goto exit;
>> +	}
>> +
>> +	/* PEC is included */
>> +	ssif_bmc->pec_support = true;
>> +	part->pec = part->payload[part->length];
>> +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +	cpec = i2c_smbus_pec(0, &addr, 1);
>> +	cpec = i2c_smbus_pec(cpec, &part->smbus_cmd, 1);
>> +	cpec = i2c_smbus_pec(cpec, &part->length, 1);
>> +	/*
>> +	 * As SMBus specification does not allow the length
>> +	 * (byte count) in the Write-Block protocol to be zero.
>> +	 * Therefore, it is illegal to have the last Middle
>> +	 * transaction in the sequence carry 32-byte and have
>> +	 * a length of ‘0’ in the End transaction.
>> +	 * But some users may try to use this way and we should
>> +	 * prevent ssif_bmc driver broken in this case.
>> +	 */
>> +	if (part->length)
>> +		cpec = i2c_smbus_pec(cpec, part->payload, part->length);
>> +
>> +	if (cpec != part->pec)
>> +		ret = false;
>> +
>> +exit:
>> +	return ret;
>> +}
>> +
>> +static void process_request_part(struct ssif_bmc_ctx *ssif_bmc) {
>> +	struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +	unsigned int len;
>> +
>> +	switch (part->smbus_cmd) {
>> +	case SSIF_IPMI_SINGLEPART_WRITE:
>> +		/* save the whole part to request*/
>> +		ssif_bmc->request.len = part->length;
>> +		memcpy(ssif_bmc->request.payload, part->payload, part->length);
>> +
>> +		break;
>> +	case SSIF_IPMI_MULTIPART_WRITE_START:
>> +		ssif_bmc->request.len = 0;
>> +
>> +		fallthrough;
>> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>> +	case SSIF_IPMI_MULTIPART_WRITE_END:
>> +		len = ssif_bmc->request.len + part->length;
>> +		/* Do the bound check here, not allow the request len exceed 254
>> bytes */
>> +		if (len > IPMI_SSIF_PAYLOAD_MAX) {
>> +			dev_warn(&ssif_bmc->client->dev,
>> +				 "Warn: Request exceeded 254 bytes, aborting");
>> +			/* Request too long, aborting */
>> +			ssif_bmc->aborting =  true;
>> +		} else {
>> +			memcpy(ssif_bmc->request.payload + ssif_bmc->request.len,
>> +			       part->payload, part->length);
>> +			ssif_bmc->request.len += part->length;
>> +		}
>> +		break;
>> +	default:
>> +		/* Do not expect to go to this case */
>> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command
>> 0x%x\n",
>> +			__func__, part->smbus_cmd);
>> +		break;
>> +	}
>> +}
>> +
>> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val) {
>> +	/* SMBUS command can vary (single or multi-part) */
>> +	ssif_bmc->part_buf.smbus_cmd = *val;
>> +	ssif_bmc->msg_idx = 1;
>> +	memset(&ssif_bmc->part_buf.payload[0], 0,
>> +MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +	if (*val == SSIF_IPMI_SINGLEPART_WRITE || *val ==
>> SSIF_IPMI_MULTIPART_WRITE_START) {
>> +		/*
>> +		 * The response maybe not come in-time, causing host SSIF driver
>> +		 * to timeout and resend a new request. In such case check for
>> +		 * pending response and clear it
>> +		 */
>> +		if (ssif_bmc->response_in_progress)
>> +			complete_response(ssif_bmc);
>> +
>> +		/* This is new request, flip aborting flag if set */
>> +		if (ssif_bmc->aborting)
>> +			ssif_bmc->aborting = false;
>> +	}
>> +}
>> +
>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8
>> +*val) {
>> +	if (ssif_bmc->state == SSIF_READY ||
>> +	    ssif_bmc->state == SSIF_START ||
>> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
>> +	    ssif_bmc->state == SSIF_RES_SENDING) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_ABORTING;
>> +		*val = 0;
>> +		return;
>> +
>> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		if (!supported_read_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>> +			dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus
>> read command=0x%x",
>> +				 ssif_bmc->part_buf.smbus_cmd);
>> +			ssif_bmc->aborting = true;
>> +		}
>> +
>> +		if (ssif_bmc->aborting)
>> +			ssif_bmc->state = SSIF_ABORTING;
>> +		else
>> +			ssif_bmc->state = SSIF_RES_SENDING;
>> +	}
>> +
>> +	ssif_bmc->msg_idx = 0;
>> +
>> +	/* Send 0 if there is nothing to send */
>> +	if (!ssif_bmc->response_in_progress || ssif_bmc->state ==
>> SSIF_ABORTING) {
>> +		*val = 0;
>> +		return;
>> +	}
>> +
>> +	if (ssif_bmc->is_singlepart_read)
>> +		set_singlepart_response_buffer(ssif_bmc);
>> +	else
>> +		set_multipart_response_buffer(ssif_bmc);
>> +
>> +	calculate_response_part_pec(&ssif_bmc->part_buf);
>> +	ssif_bmc->part_buf.index = 0;
>> +	*val = ssif_bmc->part_buf.length;
>> +}
>> +
>> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8
>> +*val) {
>> +	if (ssif_bmc->state == SSIF_READY ||
>> +	    ssif_bmc->state == SSIF_START ||
>> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
>> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_ABORTING;
>> +		*val = 0;
>> +		return;
>> +	}
>> +
>> +	/* Send 0 if there is nothing to send */
>> +	if (!ssif_bmc->response_in_progress || ssif_bmc->state ==
>> SSIF_ABORTING) {
>> +		*val = 0;
>> +		return;
>> +	}
>> +
>> +	handle_read_processed(ssif_bmc, val);
>> +}
>> +
>> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8
>> +*val) {
>> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state ==
>> SSIF_SMBUS_CMD) {
>> +		ssif_bmc->state = SSIF_START;
>> +
>> +	} else if (ssif_bmc->state == SSIF_START ||
>> +		   ssif_bmc->state == SSIF_REQ_RECVING ||
>> +		   ssif_bmc->state == SSIF_RES_SENDING) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_ABORTING;
>> +		return;
> 
> When master read here just return.
> In i2c slave device driver will not handle this.
> It may return a value to notify slave nack.
> 
Thanks Ryan for the review,

In this current implementation, Slave ignores the current transaction 
until there is new valid incoming request. My concern is that if Slave 
responses with nack would make host to retry and keep waiting response 
for the current request instead of resend a new request.

Hope to see more comments about the idea.

Thanks,
- Quan