ACK: [PATCH v3 1/1][SRU][Bionic] UBUNTU: SAUCE: at24-smbus-16bit-address
Kamal Mostafa
kamal at canonical.com
Wed Jun 3 15:51:51 UTC 2020
Thanks, Acelan.
Acked-by: Kamal Mostafa <kamal at canonical.com>
-Kamal
On Mon, Jun 01, 2020 at 01:54:31PM +0800, AceLan Kao wrote:
> From: Pieri <pierluigi.driusso at eurotech.com>
>
> BugLink: https://bugs.launchpad.net/bugs/1876699
>
> This allows to access EEPROM with 16-bit width of registers via i2c SMBus
> block functions.
>
> This commit is derivated from below commit, and then modified and provided
> by customer
> https://patchwork.ozlabs.org/patch/545292/
> Unfortunately, this commit didn't get merged into mainline in the end.
>
> From the discussion in the patch thread and another lengthy discussion[1],
> it looks like the maintainer is convinced to accept this patch[2].
> But it turns out that there is a new idea to test[3] and the result is
> not good, and the origin patch has been forgotten and didn't get merged
> in the end.
>
> In the discussion, the implementation to support access 16-bit address data
> is not safe. The multi-command sequence of the read function is not safe
> and may read the wrong data from other address if other commands are sent
> in-between the SMBus commands in the read function.
>
> 1. https://lkml.org/lkml/2015/2/4/436
> 2. https://lkml.org/lkml/2015/3/25/619
> 3. https://lkml.org/lkml/2015/3/27/99
>
> v2. add more detail description
> v3. add author's signed-off-by
>
> Signed-off-by: Pieri <pierluigi.driusso at eurotech.com>
> Signed-off-by: AceLan Kao <acelan.kao at canonical.com>
> ---
> drivers/misc/eeprom/Kconfig | 5 +-
> drivers/misc/eeprom/at24.c | 139 +++++++++++++++++++++++++++++++-----
> 2 files changed, 127 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/misc/eeprom/Kconfig b/drivers/misc/eeprom/Kconfig
> index 3f93e4564cab9..27b0e8ee04926 100644
> --- a/drivers/misc/eeprom/Kconfig
> +++ b/drivers/misc/eeprom/Kconfig
> @@ -23,7 +23,10 @@ config EEPROM_AT24
>
> If you use this with an SMBus adapter instead of an I2C adapter,
> full functionality is not available. Only smaller devices are
> - supported (24c16 and below, max 4 kByte).
> + supported via block reads (24c16 and below, max 4 kByte).
> + Larger devices that use 16-bit addresses will only work with
> + individual byte reads, which is very slow in general and is unsafe
> + in multi-master SMBus topologies.
>
> This driver can also be built as a module. If so, the module
> will be called at24.
> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> index 7554b001b502f..614b5b2c5bbd9 100644
> --- a/drivers/misc/eeprom/at24.c
> +++ b/drivers/misc/eeprom/at24.c
> @@ -3,6 +3,7 @@
> *
> * Copyright (C) 2005-2007 David Brownell
> * Copyright (C) 2008 Wolfram Sang, Pengutronix
> + * Copyright (C) 2015 Extreme Engineering Solutions, Inc.
> *
> * This program is free software; you can redistribute it and/or modify
> * it under the terms of the GNU General Public License as published by
> @@ -52,7 +53,7 @@
> * Other than binding model, current differences from "eeprom" driver are
> * that this one handles write access and isn't restricted to 24c02 devices.
> * It also handles larger devices (32 kbit and up) with two-byte addresses,
> - * which won't work on pure SMBus systems.
> + * which don't work without risks on pure SMBus systems.
> */
>
> struct at24_data {
> @@ -246,6 +247,88 @@ MODULE_DEVICE_TABLE(acpi, at24_acpi_ids);
> * one "eeprom" file not four, but larger reads would fail when
> * they crossed certain pages.
> */
> +
> +/*
> + * Write a byte to an AT24 device using SMBus cycles.
> + */
> +static inline s32 at24_smbus_write_byte_data(struct at24_data *at24,
> + struct i2c_client *client, u16 offset, u8 value)
> +{
> + if (!(at24->chip.flags & AT24_FLAG_ADDR16))
> + return i2c_smbus_write_byte_data(client, offset, value);
> +
> + /*
> + * Emulate I2C multi-byte write by using SMBus "write word"
> + * cycle. We split up the 16-bit offset among the "command"
> + * byte and the first data byte.
> + */
> + return i2c_smbus_write_word_data(client, offset >> 8,
> + (value << 8) | (offset & 0xff));
> +}
> +
> +/*
> + * Write block data to an AT24 device using SMBus cycles.
> + */
> +static inline s32 at24_smbus_write_i2c_block_data(struct at24_data *at24,
> + const struct i2c_client *client, u16 off, u8 len, const u8 *vals)
> +{
> + s32 res;
> +
> + if (!(at24->chip.flags & AT24_FLAG_ADDR16))
> + return i2c_smbus_write_i2c_block_data(client, off, len, vals);
> +
> + /* Insert extra address byte into data stream */
> + at24->writebuf[0] = off & 0xff;
> + memcpy(&at24->writebuf[1], vals, len);
> +
> + res = i2c_smbus_write_i2c_block_data(client, off >> 8, len + 1,
> + at24->writebuf);
> +
> + return res;
> +}
> +
> +/*
> + * Read block data from an AT24 device using SMBus cycles.
> + */
> +static inline s32 at24_smbus_read_block_data(struct at24_data *at24,
> + const struct i2c_client *client, u16 off, u8 len, u8 *vals)
> +{
> + int count;
> + s32 res;
> +
> + if (!(at24->chip.flags & AT24_FLAG_ADDR16))
> + return i2c_smbus_read_i2c_block_data_or_emulated(client, off,
> + len, vals);
> +
> + /*
> + * Emulate I2C multi-byte read by using SMBus "write byte" and
> + * "receive byte". This is slightly unsafe since there is an
> + * additional STOP involved, which exposes the SMBus and (this
> + * device!) to takeover by another bus master. However, it's the
> + * only way to work on SMBus-only controllers when talking to
> + * EEPROMs with multi-byte addresses.
> + */
> +
> + /* Address "dummy" write */
> + res = i2c_smbus_write_byte_data(client, off >> 8, off & 0xff);
> + if (res < 0)
> + return res;
> +
> + count = 0;
> + do {
> + /* Current Address Read */
> + res = i2c_smbus_read_byte(client);
> + if (res < 0)
> + break;
> +
> + *(vals++) = res;
> + count++;
> + len--;
> + } while (len > 0);
> +
> + return count;
> +}
> +
> static struct i2c_client *at24_translate_offset(struct at24_data *at24,
> unsigned int *offset)
> {
> @@ -286,10 +369,8 @@ static ssize_t at24_eeprom_read_smbus(struct at24_data *at24, char *buf,
> */
> read_time = jiffies;
>
> - status = i2c_smbus_read_i2c_block_data_or_emulated(client,
> - offset,
> - count, buf);
> -
> + status = at24_smbus_read_block_data(at24, client,
> + offset, count, buf);
> dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
> count, offset, status, jiffies);
>
> @@ -508,8 +589,8 @@ static ssize_t at24_eeprom_write_smbus_block(struct at24_data *at24,
> */
> write_time = jiffies;
>
> - status = i2c_smbus_write_i2c_block_data(client,
> - offset, count, buf);
> + status = at24_smbus_write_i2c_block_data(at24,
> + client, offset, count, buf);
> if (status == 0)
> status = count;
>
> @@ -543,7 +624,8 @@ static ssize_t at24_eeprom_write_smbus_byte(struct at24_data *at24,
> */
> write_time = jiffies;
>
> - status = i2c_smbus_write_byte_data(client, offset, buf[0]);
> + status = at24_smbus_write_byte_data(at24, client, offset,
> + buf[0]);
> if (status == 0)
> status = count;
>
> @@ -810,13 +892,32 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
>
> /* Use I2C operations unless we're stuck with SMBus extensions. */
> if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
> - if (chip.flags & AT24_FLAG_ADDR16)
> - return -EPFNOSUPPORT;
> -
> - if (i2c_check_functionality(client->adapter,
> + if ((chip.flags & AT24_FLAG_ADDR16) &&
> + i2c_check_functionality(client->adapter,
> + I2C_FUNC_SMBUS_READ_BYTE |
> + I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {
> + /*
> + * We need SMBUS_WRITE_BYTE_DATA and SMBUS_READ_BYTE to
> + * implement byte reads for 16-bit address devices.
> + * This will be slow, but better than nothing (e.g.
> + * read @ 3.6 KiB/s). It is also unsafe in a multi-
> + * master topology.
> + */
> + use_smbus = I2C_SMBUS_BYTE_DATA;
> + } else if (i2c_check_functionality(client->adapter,
> I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
> use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
> - } else if (i2c_check_functionality(client->adapter,
> + } else if ((chip.flags & AT24_FLAG_ADDR16) &&
> + i2c_check_functionality(client->adapter,
> + I2C_FUNC_SMBUS_WRITE_WORD_DATA)) {
> + /*
> + * We need SMBUS_WRITE_WORD_DATA to implement
> + * byte writes for 16-bit address devices.
> + */
> + use_smbus_write = I2C_SMBUS_BYTE_DATA;
> + chip.page_size = 1;
> + } else if (!(chip.flags & AT24_FLAG_ADDR16) &&
> + i2c_check_functionality(client->adapter,
> I2C_FUNC_SMBUS_READ_WORD_DATA)) {
> use_smbus = I2C_SMBUS_WORD_DATA;
> } else if (i2c_check_functionality(client->adapter,
> @@ -836,6 +937,9 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
> }
> }
>
> + if (strcmp(client->name, "24c256") == 0)
> + chip.page_size = 64;
> +
> if (chip.flags & AT24_FLAG_TAKE8ADDR)
> num_addresses = 8;
> else
> @@ -881,12 +985,15 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
> if (writable) {
> if (!use_smbus || use_smbus_write) {
>
> - unsigned write_max = chip.page_size;
> + unsigned int write_max = chip.page_size;
> + unsigned int smbus_max = (chip.flags & AT24_FLAG_ADDR16) ?
> + I2C_SMBUS_BLOCK_MAX - 1 :
> + I2C_SMBUS_BLOCK_MAX;
>
> if (write_max > io_limit)
> write_max = io_limit;
> - if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
> - write_max = I2C_SMBUS_BLOCK_MAX;
> + if (use_smbus && write_max > smbus_max)
> + write_max = smbus_max;
> at24->write_max = write_max;
>
> /* buffer (data + address at the beginning) */
> --
> 2.25.1
>
>
> --
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