Re: [PATCH v6 3/4] i2c_imc: New driver for Intel's iMC, found on LGA2011 chips

Wolfram Sang
2014-02-19T15:38:57Z

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> +config I2C_IMC
> + tristate "Intel iMC (LGA 2011) SMBus Controller"
> + depends on PCI && X86
> + select I2C_DIMM_BUS
> + help
> + If you say yes to this option, support will be included for the Intel
> + Integrated Memory Controller SMBus host controller interface. This
> + controller is found on LGA 2011 Xeons and Core i7 Extremes.
> +
> + It is possibly, although unlikely, that the use of this driver will
> + interfere with your platform's RAM thermal management.

This sounds scary and thus needs some more detail :) How does that show?
What can happen? Anything to take care of?

> @@ -15,6 +15,7 @@ obj-$(CONFIG_I2C_AMD8111) += i2c-amd8111.o
> obj-$(CONFIG_I2C_I801) += i2c-i801.o
> obj-$(CONFIG_I2C_ISCH) += i2c-isch.o
> obj-$(CONFIG_I2C_ISMT) += i2c-ismt.o
> +obj-$(CONFIG_I2C_IMC) += i2c-imc.o

This is not perfectly sorted.

> obj-$(CONFIG_I2C_NFORCE2) += i2c-nforce2.o
> obj-$(CONFIG_I2C_NFORCE2_S4985) += i2c-nforce2-s4985.o
> obj-$(CONFIG_I2C_PIIX4) += i2c-piix4.o
> diff --git a/drivers/i2c/busses/i2c-imc.c b/drivers/i2c/busses/i2c-imc.c
> new file mode 100644
> index 0000000..c846077
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-imc.c
> @@ -0,0 +1,559 @@
> +/*
> + * Copyright (c) 2013 Andrew Lutomirski <luto@amacapital.net>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Please skip the address. And run checkpatch.pl --strict! It would have
warned you about this and other stuff:

total: 1 errors, 3 warnings, 2 checks, 587 lines checked

> +/*
> + * The datasheet can be found here, for example:
> + * http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-1600-2600-vol-2-datasheet.pdf
> + *
> + * There seem to be quite a few bugs or spec errors, though:

Kudos for the useful comments!

> +/* Register offsets (in PCI configuration space) */
> +#define SMBSTAT(i) (0x180 + 0x10*i)
> +#define SMBCMD(i) (0x184 + 0x10*i)
> +#define SMBCNTL(i) (0x188 + 0x10*i)
> +#define SMB_TSOD_POLL_RATE_CNTR(i) (0x18C + 0x10*i)
> +#define SMB_TSOD_POLL_RATE (0x1A8)

Spaces around operators!

> + int i;
> + for (i = 0; i < 50; i++) {
> + pci_read_config_dword(priv->pci_dev, SMBSTAT(chan), stat);
> + if (!(*stat & SMBSTAT_SMB_BUSY))
> + return 0;
> + udelay(70);

usleep_range?

> + }
> +
> + return -ETIMEDOUT;
> +}
> +

...

> +static s32 imc_smbus_xfer(struct i2c_adapter *adap, u16 addr,
> + unsigned short flags, char read_write, u8 command,
> + int size, union i2c_smbus_data *data)
> +{
> + int ret, chan;
> + u32 cmd = 0, cntl, final_cmd, final_cntl, stat;
> + struct imc_channel *ch;
> + struct imc_priv *priv = i2c_get_adapdata(adap);
> +
> + if (atomic_read(&imc_raced))
> + return -EIO; /* Minimize damage. */
> +
> + chan = (adap == &priv->channels[0].adapter ? 0 : 1);
> + ch = &priv->channels[chan];
> +
> + if (addr > 0x7f)
> + return -EOPNOTSUPP; /* No large address support */

Unneeded. The core checks for that...

> + if (flags)
> + return -EOPNOTSUPP; /* No PEC */

... and your code would bail out if I2C_M_TEN was set.

> + if (size != I2C_SMBUS_BYTE_DATA && size != I2C_SMBUS_WORD_DATA)
> + return -EOPNOTSUPP;
> +
> + /* Encode CMD part of addresses and access size */
> + cmd |= ((u32)addr & 0x7) << SMBCMD_SA_SHIFT;
> + cmd |= ((u32)command) << SMBCMD_BA_SHIFT;
> + if (size == I2C_SMBUS_WORD_DATA)
> + cmd |= SMBCMD_WORD_ACCESS;
> +
> + /* Encode read/write and data to write */
> + if (read_write == I2C_SMBUS_READ) {
> + cmd |= SMBCMD_TYPE_READ;
> + } else {
> + cmd |= SMBCMD_TYPE_WRITE;
> + cmd |= (size == I2C_SMBUS_WORD_DATA
> + ? swab16(data->word)
> + : data->byte);
> + }
> +
> + mutex_lock(&ch->mutex);

Why is the per-adapter lock not sufficient?

> +
> + ret = imc_channel_claim(priv, chan);
> + if (ret)
> + goto out_unlock;
> +
> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &cntl);
> + cntl &= ~SMBCNTL_DTI_MASK;
> + cntl |= ((u32)addr >> 3) << SMBCNTL_DTI_SHIFT;
> + pci_write_config_dword(priv->pci_dev, SMBCNTL(chan), cntl);
> +
> + /*
> + * This clears SMBCMD_PNTR_SEL. We leave it cleared so that we don't
> + * need to think about keeping the TSOD pointer state consistent with
> + * the hardware's expectation. This probably has some miniscule
> + * power cost, as TSOD polls will take 9 extra cycles.
> + */
> + cmd |= SMBCMD_TRIGGER;
> + pci_write_config_dword(priv->pci_dev, SMBCMD(chan), cmd);
> +
> + if (imc_wait_not_busy(priv, chan, &stat) != 0) {
> + /* Timeout. TODO: Reset the controller? */
> + ret = -EIO;
> + dev_err(&priv->pci_dev->dev, "controller is wedged\n");
> + goto out_release;
> + }
> +
> + /*
> + * Be paranoid: try to detect races. This will only detect races
> + * against BIOS, not against hardware. (I've never seen this happen.)
> + */
> + pci_read_config_dword(priv->pci_dev, SMBCMD(chan), &final_cmd);
> + pci_read_config_dword(priv->pci_dev, SMBCNTL(chan), &final_cntl);
> + if (((cmd ^ final_cmd) & SMBCMD_OUR_BITS) ||
> + ((cntl ^ final_cntl) & SMBCNTL_OUR_BITS)) {
> + WARN(1, "iMC SMBUS raced against firmware");
> + dev_emerg(&priv->pci_dev->dev,
> + "Access to channel %d raced: cmd 0x%08X->0x%08X, cntl 0x%08X->0x%08X\n",
> + chan, cmd, final_cmd, cntl, final_cntl);

Ehrm, do we need WARN and dev_emerg? And the error message should be
updated. It should tell what the user should do next to handle the
emergency.

...

> + if (!imc_channel_can_claim(priv, i)) {
> + dev_warn(&priv->pci_dev->dev,
> + "iMC channel %d: we cannot control the HW. Is CLTT on?\n",
> + i);

That should go on the previous line IMO. The 80 char limit may be broken
for readability reasons.

> +MODULE_AUTHOR("Andrew Lutomirski <luto@amacapital.net>");
> +MODULE_DESCRIPTION("iMC SMBus driver");
> +MODULE_LICENSE("GPL");

GPL v2 according to header.

Thanks,

Wolfram

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