Subject: Re: [PATCH v11 14/14] hwmon: Add PECI dimmtemp driver

From: Guenter Roeck <[email-masked]>
Date: Mon, 16 Dec 2019 15:27:20 -0800

On Mon, Dec 16, 2019 at 02:17:34PM -0800, Jae Hyun Yoo wrote:
> [...]
> 
> > > > > +static int get_dimm_temp(struct peci_dimmtemp *priv, int dimm_no)
> > > > > +{
> > > > > +    int dimm_order = dimm_no % priv->gen_info->dimm_idx_max;
> > > > > +    int chan_rank = dimm_no / priv->gen_info->dimm_idx_max;
> > > > > +    struct peci_rd_pci_cfg_local_msg rp_msg;
> > > > > +    u8  cfg_data[4];
> > > > > +    int ret;
> > > > > +
> > > > > +    if (!peci_sensor_need_update(&priv->temp[dimm_no]))
> > > > > +        return 0;
> > > > > +
> > > > > +    ret = read_ddr_dimm_temp_config(priv, chan_rank, cfg_data);
> > > > > +    if (ret)
> > > > > +        return ret;
> > > > > +
> > > > > +    priv->temp[dimm_no].value = cfg_data[dimm_order] * 1000;
> > > > > +
> > > > > +    switch (priv->gen_info->model) {
> > > > > +    case INTEL_FAM6_SKYLAKE_X:
> > > > > +        rp_msg.addr = priv->mgr->client->addr;
> > > > > +        rp_msg.bus = 2;
> > > > > +        /*
> > > > > +         * Device 10, Function 2: IMC 0 channel 0 -> rank 0
> > > > > +         * Device 10, Function 6: IMC 0 channel 1 -> rank 1
> > > > > +         * Device 11, Function 2: IMC 0 channel 2 -> rank 2
> > > > > +         * Device 12, Function 2: IMC 1 channel 0 -> rank 3
> > > > > +         * Device 12, Function 6: IMC 1 channel 1 -> rank 4
> > > > > +         * Device 13, Function 2: IMC 1 channel 2 -> rank 5
> > > > > +         */
> > > > > +        rp_msg.device = 10 + chan_rank / 3 * 2 +
> > > > > +                 (chan_rank % 3 == 2 ? 1 : 0);
> > > > > +        rp_msg.function = chan_rank % 3 == 1 ? 6 : 2;
> > > > > +        rp_msg.reg = 0x120 + dimm_order * 4;
> > > > > +        rp_msg.rx_len = 4;
> > > > > +
> > > > > +        ret = peci_command(priv->mgr->client->adapter,
> > > > > +                   PECI_CMD_RD_PCI_CFG_LOCAL, &rp_msg);
> > > > > +        if (rp_msg.cc != PECI_DEV_CC_SUCCESS)
> > > > > +            ret = -EAGAIN;
> > > > > +        if (ret)
> > > > > +            return ret;
> > > > > +
> > > > > +        priv->temp_max[dimm_no] = rp_msg.pci_config[1] * 1000;
> > > > > +        priv->temp_crit[dimm_no] = rp_msg.pci_config[2] * 1000;
> > > > > +        break;
> > > > > +    case INTEL_FAM6_SKYLAKE_XD:
> > > > > +        rp_msg.addr = priv->mgr->client->addr;
> > > > > +        rp_msg.bus = 2;
> > > > > +        /*
> > > > > +         * Device 10, Function 2: IMC 0 channel 0 -> rank 0
> > > > > +         * Device 10, Function 6: IMC 0 channel 1 -> rank 1
> > > > > +         * Device 12, Function 2: IMC 1 channel 0 -> rank 2
> > > > > +         * Device 12, Function 6: IMC 1 channel 1 -> rank 3
> > > > > +         */
> > > > > +        rp_msg.device = 10 + chan_rank / 2 * 2;
> > > > > +        rp_msg.function = (chan_rank % 2) ? 6 : 2;
> > > > > +        rp_msg.reg = 0x120 + dimm_order * 4;
> > > > > +        rp_msg.rx_len = 4;
> > > > > +
> > > > > +        ret = peci_command(priv->mgr->client->adapter,
> > > > > +                   PECI_CMD_RD_PCI_CFG_LOCAL, &rp_msg);
> > > > > +        if (rp_msg.cc != PECI_DEV_CC_SUCCESS)
> > > > > +            ret = -EAGAIN;
> > > > > +        if (ret)
> > > > > +            return ret;
> > > > > +
> > > > > +        priv->temp_max[dimm_no] = rp_msg.pci_config[1] * 1000;
> > > > > +        priv->temp_crit[dimm_no] = rp_msg.pci_config[2] * 1000;
> > > > > +        break;
> > > > > +    case INTEL_FAM6_HASWELL_X:
> > > > > +    case INTEL_FAM6_BROADWELL_X:
> > > > > +        rp_msg.addr = priv->mgr->client->addr;
> > > > > +        rp_msg.bus = 1;
> > > > > +        /*
> > > > > +         * Device 20, Function 0: IMC 0 channel 0 -> rank 0
> > > > > +         * Device 20, Function 1: IMC 0 channel 1 -> rank 1
> > > > > +         * Device 21, Function 0: IMC 0 channel 2 -> rank 2
> > > > > +         * Device 21, Function 1: IMC 0 channel 3 -> rank 3
> > > > > +         * Device 23, Function 0: IMC 1 channel 0 -> rank 4
> > > > > +         * Device 23, Function 1: IMC 1 channel 1 -> rank 5
> > > > > +         * Device 24, Function 0: IMC 1 channel 2 -> rank 6
> > > > > +         * Device 24, Function 1: IMC 1 channel 3 -> rank 7
> > > > > +         */
> > > > > +        rp_msg.device = 20 + chan_rank / 2 + chan_rank / 4;
> > > > > +        rp_msg.function = chan_rank % 2;
> > > > > +        rp_msg.reg = 0x120 + dimm_order * 4;
> > > > > +        rp_msg.rx_len = 4;
> > > > > +
> > > > > +        ret = peci_command(priv->mgr->client->adapter,
> > > > > +                   PECI_CMD_RD_PCI_CFG_LOCAL, &rp_msg);
> > > > > +        if (rp_msg.cc != PECI_DEV_CC_SUCCESS)
> > > > > +            ret = -EAGAIN;
> > > > > +        if (ret)
> > > > > +            return ret;
> > > > > +
> > > > > +        priv->temp_max[dimm_no] = rp_msg.pci_config[1] * 1000;
> > > > > +        priv->temp_crit[dimm_no] = rp_msg.pci_config[2] * 1000;
> > > > > +        break;
> > > > > +    default:
> > > > > +        return -EOPNOTSUPP;
> > > > 
> > > > It looks like the sensors are created even on unsupported platforms,
> > > > which would generate error messages whenever someone tries to read
> > > > the attributes.
> > > > 
> > > > There should be some code early on checking this, and the driver
> > > > should not even instantiate if the CPU model is not supported.
> > > 
> > > Actually, this 'default' case will not be happened because this driver
> > > will be registered only when the CPU model is supported. The CPU model
> > > checking code is in 'intel-peci-client.c' which is [11/14] of this
> > > patch set.
> > > 
> > 
> > That again assumes that both drivers will be modified in sync in the future.
> > We can not make that assumption.
> 
> As you said, both drivers must be modified in sync in the future because
> each Intel CPU family uses different way of reading DIMM temperature.
> In case if supported CPU checking code updated without making sync with
> it, this driver will return the error.
> 

... and in that situation the driver should not instantiate in the
first place. Its probe function should return -ENODEV.

Guenter

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