Re: [PATCH v3 2/2] fsi: Add IBM I2C Responder virtual FSI master

[Eddie James <eajames@linux.ibm.com>]

On 1/26/23 19:25, Andrew Jeffery wrote:
> Hi Eddie,
>
> On Fri, 27 Jan 2023, at 08:01, Eddie James wrote:
>> The I2C Responder (I2CR) is an I2C device that translates I2C commands
>> to CFAM or SCOM operations, effectively implementing an FSI master and
>> bus.
>>
>> Signed-off-by: Eddie James <eajames@linux.ibm.com>
>> ---
>>   drivers/fsi/Kconfig                    |   9 +
>>   drivers/fsi/Makefile                   |   1 +
>>   drivers/fsi/fsi-master-i2cr.c          | 225 +++++++++++++++++++++++++
>>   include/trace/events/fsi_master_i2cr.h |  96 +++++++++++
>>   4 files changed, 331 insertions(+)
>>   create mode 100644 drivers/fsi/fsi-master-i2cr.c
>>   create mode 100644 include/trace/events/fsi_master_i2cr.h
>>
>> diff --git a/drivers/fsi/Kconfig b/drivers/fsi/Kconfig
>> index e6668a869913..999be82720c5 100644
>> --- a/drivers/fsi/Kconfig
>> +++ b/drivers/fsi/Kconfig
>> @@ -62,6 +62,15 @@ config FSI_MASTER_ASPEED
>>
>>   	 Enable it for your BMC kernel in an OpenPower or IBM Power system.
>>
>> +config FSI_MASTER_I2CR
>> +	tristate "IBM I2C Responder virtual FSI master"
>> +	depends on I2C
>> +	help
>> +	  This option enables a virtual FSI master in order to access a CFAM
>> +	  behind an IBM I2C Responder (I2CR) chip. The I2CR is an I2C device
>> +	  that translates I2C commands to CFAM or SCOM operations, effectively
>> +	  implementing an FSI master and bus.
>> +
>>   config FSI_SCOM
>>   	tristate "SCOM FSI client device driver"
>>   	help
>> diff --git a/drivers/fsi/Makefile b/drivers/fsi/Makefile
>> index da218a1ad8e1..34dbaa1c452e 100644
>> --- a/drivers/fsi/Makefile
>> +++ b/drivers/fsi/Makefile
>> @@ -4,6 +4,7 @@ obj-$(CONFIG_FSI) += fsi-core.o
>>   obj-$(CONFIG_FSI_MASTER_HUB) += fsi-master-hub.o
>>   obj-$(CONFIG_FSI_MASTER_ASPEED) += fsi-master-aspeed.o
>>   obj-$(CONFIG_FSI_MASTER_GPIO) += fsi-master-gpio.o
>> +obj-$(CONFIG_FSI_MASTER_I2CR) += fsi-master-i2cr.o
>>   obj-$(CONFIG_FSI_MASTER_AST_CF) += fsi-master-ast-cf.o
>>   obj-$(CONFIG_FSI_SCOM) += fsi-scom.o
>>   obj-$(CONFIG_FSI_SBEFIFO) += fsi-sbefifo.o
>> diff --git a/drivers/fsi/fsi-master-i2cr.c
>> b/drivers/fsi/fsi-master-i2cr.c
>> new file mode 100644
>> index 000000000000..0eadc9b26063
>> --- /dev/null
>> +++ b/drivers/fsi/fsi-master-i2cr.c
>> @@ -0,0 +1,225 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (C) IBM Corporation 2023 */
>> +
>> +#include <linux/device.h>
>> +#include <linux/fsi.h>
>> +#include <linux/i2c.h>
>> +#include <linux/module.h>
>> +#include <linux/mod_devicetable.h>
>> +#include <linux/mutex.h>
>> +
>> +#include "fsi-master.h"
>> +
>> +#define CREATE_TRACE_POINTS
>> +#include <trace/events/fsi_master_i2cr.h>
>> +
>> +#define I2CR_ADDRESS_CFAM(a)	((a) >> 2)
>> +#define I2CR_STATUS		0x30001
>> +#define  I2CR_STATUS_ERR	 BIT_ULL(61)
>> +#define I2CR_ERROR		0x30002
>> +
>> +struct fsi_master_i2cr {
>> +	struct fsi_master master;
>> +	struct mutex lock;	/* protect HW access */
>> +	struct i2c_client *client;
>> +};
>> +
>> +static bool i2cr_check_parity(u32 v, bool parity)
>> +{
>> +	u32 i;
>> +
>> +	for (i = 0; i < 32; ++i) {
>> +		if (v & (1 << i))
>> +			parity = !parity;
>> +	}
>> +
>> +	return parity;
>> +}
>> +
>> +static __be32 i2cr_get_command(u32 address, bool parity)
>> +{
>> +	__be32 command;
>> +
>> +	address <<= 1;
>> +
>> +	if (i2cr_check_parity(address, parity))
>> +		address |= 1;
>> +
>> +	command = cpu_to_be32(address);
>> +	trace_i2cr_command((__force uint32_t)command);
>> +
>> +	return command;
>> +}
>> +
>> +static int i2cr_transfer(struct i2c_client *client, u32 address,
>> __be64 *data)
>> +{
>> +	struct i2c_msg msgs[2];
>> +	__be32 command;
>> +	int ret;
>> +
>> +	command = i2cr_get_command(address, true);
>> +	msgs[0].addr = client->addr;
>> +	msgs[0].flags = 0;
>> +	msgs[0].len = sizeof(command);
>> +	msgs[0].buf = (__u8 *)&command;
>> +	msgs[1].addr = client->addr;
>> +	msgs[1].flags = I2C_M_RD;
>> +	msgs[1].len = sizeof(*data);
>> +	msgs[1].buf = (__u8 *)data;
>> +
>> +	ret = i2c_transfer(client->adapter, msgs, 2);
>> +	if (ret == 2)
>> +		return 0;
>> +
>> +	trace_i2cr_i2c_error(ret);
>> +
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	return -EIO;
>> +}
>> +
>> +static int i2cr_check_status(struct i2c_client *client)
>> +{
>> +	__be64 status_be = 0;
>> +	u64 status;
>> +	int ret;
>> +
>> +	ret = i2cr_transfer(client, I2CR_STATUS, &status_be);
>> +	if (ret)
>> +		return ret;
>> +
>> +	status = be64_to_cpu(status_be);
>> +	if (status & I2CR_STATUS_ERR) {
>> +		__be64 error_be = 0;
>> +		u64 error;
>> +
>> +		i2cr_transfer(client, I2CR_ERROR, &error_be);
>> +		error = be64_to_cpu(error_be);
>> +		trace_i2cr_status_error(status, error);
>> +		dev_err(&client->dev, "status:%016llx error:%016llx\n", status,
>> error);
>> +		return -EREMOTEIO;
>> +	}
>> +
>> +	trace_i2cr_status(status);
>> +	return 0;
>> +}
>> +
>> +static int i2cr_read(struct fsi_master *master, int link, uint8_t id,
>> uint32_t addr, void *val,
>> +		     size_t size)
>> +{
>> +	struct fsi_master_i2cr *i2cr = container_of(master, struct
>> fsi_master_i2cr, master);
>> +	__be64 data = 0;
>> +	int ret;
>> +
>> +	if (link || id || (addr & 0xffff0000) || !(size == 1 || size == 2 ||
>> size == 4))
>> +		return -EINVAL;
>> +
>> +	mutex_lock(&i2cr->lock);
>> +
>> +	ret = i2cr_transfer(i2cr->client, I2CR_ADDRESS_CFAM(addr), &data);
>> +	if (ret)
>> +		goto unlock;
>> +
>> +	ret = i2cr_check_status(i2cr->client);
>> +	if (ret)
>> +		goto unlock;
>> +
>> +	trace_i2cr_read(addr, size, (__force uint32_t)data);
>> +	memcpy(val, &data, size);
>> +
>> +unlock:
>> +	mutex_unlock(&i2cr->lock);
>> +	return ret;
>> +}
>> +
>> +static int i2cr_write(struct fsi_master *master, int link, uint8_t id,
>> uint32_t addr,
>> +		      const void *val, size_t size)
>> +{
>> +	struct fsi_master_i2cr *i2cr = container_of(master, struct
>> fsi_master_i2cr, master);
>> +	struct {
>> +		__be32 command;
>> +		u32 val;
>> +		u32 rsvd;
>> +	} __packed data = { 0, 0, 0 };
>> +	int ret;
>> +
>> +	if (link || id || (addr & 0xffff0000) || !(size == 1 || size == 2 ||
>> size == 4))
>> +		return -EINVAL;
>> +
>> +	memcpy(&data.val, val, size);
> Still nervous about endian mixups here given the buffers in val tend to
> be pointers to big-endian values but data.val is native-endian (likely
> little-endian). It probably doesn't matter functionally given we pass
> the pointer to the packed struct through i2c_master_send(), but do the
> values come out right in the trace data?
>
> What do you think about adding some commentary outlining the value
> representations to help with confidence here?


Yea, this is still not the cleanest. I'll either add comments or rework 
it a little bit. I have reworked the trace functions to get rid of any 
casting too.


>
>> +	data.command = i2cr_get_command(I2CR_ADDRESS_CFAM(addr),
>> +					i2cr_check_parity(data.val, true));
>> +
>> +	mutex_lock(&i2cr->lock);
>> +
>> +	ret = i2c_master_send(i2cr->client, (const char *)&data,
>> sizeof(data));
>> +	if (ret == sizeof(data)) {
>> +		ret = i2cr_check_status(i2cr->client);
>> +		if (!ret)
>> +			trace_i2cr_write(addr, size, data.val);
>> +	} else {
>> +		trace_i2cr_i2c_error(ret);
>> +
>> +		if (ret >= 0)
>> +			ret = -EIO;
>> +	}
> The i2cr_transfer() call in i2cr_check_status() can error but that
> won't be traced. Is that intentional? What about this instead?


i2cr_transfer itself traces on i2c error, so we should be covered? In 
your snippet below, you'll get an "i2cr_i2c_error" trace even for a 
failed status check, which isn't my intention for that function.


Thanks for the review!

Eddie


>
> ret = i2c_master_send(...)
> if (ret == sizeof(data)) {
>      ret = i2cr_check_status(i2cr->client);
> } else {
>      ret = -EIO;
> }
>
> if (ret) {
>      trace_i2cr_i2c_error(ret);
> } else {
>      trace_i2cr_write(addr, size, data.val);
> }
>
> Cheers,
>
> Andrew