Date:   Mon, 13 Sep 2021 00:41:02 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Avri Altman <Avri.Altman@....com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bart Van Assche <bvanassche@....org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Bean Huo <beanhuo@...ron.com>
Subject: Re: [PATCH v3 1/2] scsi: ufs: Probe for temperature notification
 support

On 9/13/21 12:06 AM, Avri Altman wrote:
>>> +config SCSI_UFS_HWMON
>>> +     bool "UFS  Temperature Notification"
>>> +     depends on SCSI_UFSHCD && HWMON
>>> +     help
>>> +       This provides support for UFS hardware monitoring. If enabled,
>>> +       a hardware monitoring device will be created for the UFS device.
>>> +
>>> +       If unsure, say N.
>>> +
>>
>> git complains about blank line at EOF.
> Done.
> 
>>
>>> diff --git a/drivers/scsi/ufs/Makefile b/drivers/scsi/ufs/Makefile
>>> index c407da9b5171..966048875b50 100644
>>> --- a/drivers/scsi/ufs/Makefile
>>> +++ b/drivers/scsi/ufs/Makefile
>>> @@ -10,6 +10,7 @@ ufshcd-core-$(CONFIG_SCSI_UFS_BSG)  += ufs_bsg.o
>>>    ufshcd-core-$(CONFIG_SCSI_UFS_CRYPTO)       += ufshcd-crypto.o
>>>    ufshcd-core-$(CONFIG_SCSI_UFS_HPB)  += ufshpb.o
>>>    ufshcd-core-$(CONFIG_SCSI_UFS_FAULT_INJECTION) +=
>>> ufs-fault-injection.o
>>> +ufshcd-core-$(CONFIG_SCSI_UFS_HWMON) += ufs-hwmon.o
>>>
>>>    obj-$(CONFIG_SCSI_UFS_DWC_TC_PCI) += tc-dwc-g210-pci.o ufshcd-dwc.o
>> tc-dwc-g210.o
>>>    obj-$(CONFIG_SCSI_UFS_DWC_TC_PLATFORM) += tc-dwc-g210-pltfrm.o
>>> ufshcd-dwc.o tc-dwc-g210.o diff --git a/drivers/scsi/ufs/ufs-hwmon.c
>>> b/drivers/scsi/ufs/ufs-hwmon.c new file mode 100644 index
>>> 000000000000..a50e83f645f4
>>> --- /dev/null
>>> +++ b/drivers/scsi/ufs/ufs-hwmon.c
>>> @@ -0,0 +1,179 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * UFS hardware monitoring support
>>> + * Copyright (c) 2021, Western Digital Corporation  */
>>> +
>>> +#include <linux/hwmon.h>
>>> +
>>> +#include "ufshcd.h"
>>> +
>>> +struct ufs_hwmon_data {
>>> +     struct ufs_hba *hba;
>>> +     u8 mask;
>>> +};
>>> +
>>> +static bool ufs_temp_enabled(struct ufs_hba *hba, u8 mask) {
>>> +     u32 ee_mask;
>>> +
>>> +     if (ufshcd_query_attr(hba, UPIU_QUERY_OPCODE_READ_ATTR,
>>> +                           QUERY_ATTR_IDN_EE_CONTROL, 0, 0, &ee_mask))
>>> +             return false;
>>> +
>>> +     return (mask & ee_mask & MASK_EE_TOO_HIGH_TEMP) ||
>>> +             (mask & ee_mask & MASK_EE_TOO_LOW_TEMP); }
>>> +
>>> +static bool ufs_temp_valid(struct ufs_hba *hba, u8 mask,
>>> +                        enum attr_idn idn, u32 value) {
>>> +     return (idn == QUERY_ATTR_IDN_CASE_ROUGH_TEMP && value >= 1
>> &&
>>> +             value <= 250 && ufs_temp_enabled(hba, mask)) ||
>>> +           (idn == QUERY_ATTR_IDN_HIGH_TEMP_BOUND && value >= 100 &&
>>> +            value <= 250) ||
>>> +           (idn == QUERY_ATTR_IDN_LOW_TEMP_BOUND && value >= 1 &&
>>> +            value <= 80);
>>> +}
>>> +
>> The value ranges checed above suggest that the temperature is reported in
>> degrees C (or maybe degrees C with an offset).
> Yes.  No offset.
> 
>> The hwmon API expects
>> temperatures to be reported in milli-degrees C, and I don't see a conversion in
>> the actual read functions. What does the "sensors" command report ?
> I missed that (Although it is well documented) - sorry about that.
> I wasn't aware of the sensors command.  I don't have it in my arm64 android platform image (galaxy s21).
> Will try to get it.
> I was reading the temperature using hwmon sysfs entries, which indicate the correct temperature.
> e.g
> t2s:/ # ls -la /sys/class/hwmon/
> total 0
> drwxr-xr-x   2 root root 0 2020-12-20 10:16 .
> drwxr-xr-x 104 root root 0 2020-12-19 19:05 ..
> lrwxrwxrwx   1 root root 0 2020-12-20 10:16 hwmon0 -> ../../devices/platform/13100000.ufs/hwmon/hwmon0
> .....
> 
> t2s:/ # cat /sys/class/hwmon/hwmon0/temp1_input
> 25
> 
> Will fix it.  Thanks.
> 
>>
>>> +static int ufs_get_temp(struct ufs_hba *hba, u8 mask, enum attr_idn
>>> +idn) {
>>> +     u32 value;
>>> +
>>> +     if (ufshcd_query_attr(hba, UPIU_QUERY_OPCODE_READ_ATTR, idn, 0, 0,
>>> +         &value))
>>
>> checkpatch states that alignment is off, and I am quite sure this fits into one
>> line anyway (with the 100-column limit). There are more instances with bad
>> alignment according to checkpatch.
> I wasn't aware that the Linux Kernel deprecates the 80 Character Line Coding Style.
> Will try to make it full 100-characters lines.
> I didn't get any alignment complaints from checkpatch.
> 
>>
>> Also, ufshcd_query_attr() returns a valid Linux error code. That should be
>> returned to the caller and not be replaced. More on that below.
>>
>>> +             return 0;
>>> +
>>> +     if (ufs_temp_valid(hba, mask, idn, value))
>>> +             return value - 80;
>>> +
>>
>> This again suggests that the temperature is not milli-degrees C.
>>
>> Is there reason to believe that this validation is necessary ?
>> Note that this reports an "error" if the returned temperature value happens to
>> have a value of 80. Again, more on that below.
> Data->mask holds the temperature related bits in the ufs features register: TOO_LOW_TEMPERATURE and TOO_HIGH_TEMPERATURE.
> This is set for the device by the flash vendor and can't be changed by the OEMs.
> If the device doesn't support any of that, then hwmon_probe is not even called, see ufshcd_temp_notif_probe.
> So data->mask is not 0, and never changes.
> 
> When the device returns a 0 temperature value, it means that it is not valid.
> The spec say about the Device’s rough package case surface temperature:
> "
> This value shall be valid when (TOO_HIGH_TEMPERATURE is supported and TOO_HIGH_TEMP_EN is enabled) or
> ( TOO_LOW_TEMPERATURE is supported and TOO_LOW_TEMP_EN is enabled ).
> 0 : Unknown Temperature , 1~250 : ( this value – 80 ) degrees in Celsius. ( i.e., -79 ºC ~ 170 ºC )
> Others: Reserved
> "
> data->mask is not 0, but the temperature exception bits: TOO_HIGH_TEMP_EN and TOO_LOW_TEMP_EN are of type read/volatile,
> Meaning it can be written many times, e.g. by debugfs or ufs-utils.
> 
> To sum up:
>   - yes, checking the temperature against the spec boundaries is useless.
>     The device will return 0 if it is not valid.
>     ufs_temp_valid() can be removed, and just need to check that the temperature is not 0.
> 
>   - The return value of querry_attr is of less interest.
>      if it failed or temp == 0, then the temperature is invalid and the proper return value should be -EINVAL.
> 
>>
>>> +     return 0;
>>> +}
>>> +
>>> +static int ufs_hwmon_read(struct device *dev, enum hwmon_sensor_types
>> type,
>>> +                        u32 attr, int channel, long *val) {
>>> +     struct ufs_hwmon_data *data = dev_get_drvdata(dev);
>>> +     struct ufs_hba *hba = data->hba;
>>> +     u8 mask = data->mask;
>>> +     int err = 0;
>>> +     bool get_temp = true;
>>> +
>>> +     if (type != hwmon_temp)
>>> +             return 0;
>>> +
>>> +     down(&hba->host_sem);
>>> +
>>> +     if (!ufshcd_is_user_access_allowed(hba)) {
>>> +             up(&hba->host_sem);
>>> +             return -EBUSY;
>>> +     }
>>> +
>>> +     ufshcd_rpm_get_sync(hba);
>>> +
>>> +     switch (attr) {
>>> +     case hwmon_temp_enable:
>>> +             *val = ufs_temp_enabled(hba, mask);
>>> +             get_temp = false;
>>> +
>>
>> This seems to be read-only, and the mask only affects the limit registers as far
>> as I con see. If so, this is wrong: The mask should be used to enable or hide the
>> limit attributes as needed. If the mask is 0, and if this means that the current
>> temperature is not reported either, the driver should not instantiate at all.
>>
>> The "enable" attribute only makes sense if it can be used to actually enable or
>> disable a specific sensor, and is not tied to limit attributes but to the actual
>> sensor values.
> See explanation above.
>   Will make it writable as well.
> 

That only makes sense if the information is passed to the chip. What is going
to happen if the user writes 0 into the attribute ?

Guenter

>>
>>> +             break;
>>> +     case hwmon_temp_max_alarm:
>>> +             *val = ufs_get_temp(hba, mask,
>>> + QUERY_ATTR_IDN_HIGH_TEMP_BOUND);
>>> +
>>> +             break;
>>> +     case hwmon_temp_min_alarm:
>>> +             *val = ufs_get_temp(hba, mask,
>>> + QUERY_ATTR_IDN_LOW_TEMP_BOUND);
>>> +
>>> +             break;
>>> +     case hwmon_temp_input:
>>> +             *val = ufs_get_temp(hba, mask,
>>> + QUERY_ATTR_IDN_CASE_ROUGH_TEMP);
>>> +
>> If an enable attribute exists and is 0 (disabled), this should return -ENODATA.
>> In this case, that would imply that the driver should not be instantiated in the
>> first place since it has nothing to report.
> See explanation above.
> Will fix it so the error value will make more sense.
> 
>>
>>> +             break;
>>> +     default:
>>> +             err = -EOPNOTSUPP;
>>> +
>>> +             break;
>>> +     }
>>> +
>>> +     ufshcd_rpm_put_sync(hba);
>>> +
>>> +     up(&hba->host_sem);
>>> +
>>> +     if (get_temp && !err && *val == 0)
>>> +             err = -EINVAL;
>>> +
>> That is an odd way of detection errors. If it was in the hwmon subsystem, I'd ask
>> for the error handling to be moved into the case statements. On top of that,
>> interpreting a return value of "0" as error seems wrong.
>> ufs_get_temp() returns 0 if the measured temperature or the reported limit
>> happens to have a value of 80, and that is perfectly valid. If ufs_get_temp()
>> reports an error, it should report that as error.
>>
>> Also, EINVAL is "invalid argument", which I am quite sure does not apply here.
> Ditto.
> EINVAL implies that the temperature is invalid.
> 
>>>
>>> +static void ufshcd_temp_notif_probe(struct ufs_hba *hba, u8
>>> +*desc_buf) {
>>> +     struct ufs_dev_info *dev_info = &hba->dev_info;
>>> +     u32 ext_ufs_feature;
>>> +     u8 mask = 0;
>>> +
>>> +     if (!(hba->caps & UFSHCD_CAP_TEMP_NOTIF) ||
>>> +         dev_info->wspecversion < 0x300)
>>
>> I am quite sure this fits a single line.
> Done.
> 

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