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Date:   Thu, 1 Sep 2022 12:25:16 -0700
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Subject: Re: [PATCH v3 02/19] hwmon: (mr75203) fix VM sensor allocation when
 "intel, vm-map" not defined
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To:     "Farber, Eliav" <farbere@amazon.com>
Cc:     jdelvare@suse.com, robh+dt@kernel.org, p.zabel@pengutronix.de,
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From:   Guenter Roeck <linux@roeck-us.net>
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On 9/1/22 11:36, Farber, Eliav wrote:
> On 9/1/2022 8:11 PM, Guenter Roeck wrote:
>> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>>
>>
>>
>> On 9/1/22 08:24, Farber, Eliav wrote:
>>> On 9/1/2022 5:44 PM, Guenter Roeck wrote:
>>>> On Thu, Sep 01, 2022 at 11:39:58AM +0300, Farber, Eliav wrote:
>>>>> On 8/31/2022 2:48 PM, Guenter Roeck wrote:
>>>>> > On 8/30/22 22:49, Farber, Eliav wrote:
>>>>> > > On 8/31/2022 8:36 AM, Guenter Roeck wrote:
>>>>> > > > On 8/30/22 12:21, Eliav Farber wrote:
>>>>> > > > > Bug fix - in case "intel,vm-map" is missing in device-tree
>>>>> > > > > ,'num' is set
>>>>> > > > > to 0, and no voltage channel infos are allocated.
>>>>> > > > >
>>>>> > > > > Signed-off-by: Eliav Farber <farbere@amazon.com>
>>>>> > > > > ---
>>>>> > > > >   drivers/hwmon/mr75203.c | 28 ++++++++++++----------------
>>>>> > > > >   1 file changed, 12 insertions(+), 16 deletions(-)
>>>>> > > > >
>>>>> > > > > diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c
>>>>> > > > > index 046523d47c29..0e29877a1a9c 100644
>>>>> > > > > --- a/drivers/hwmon/mr75203.c
>>>>> > > > > +++ b/drivers/hwmon/mr75203.c
>>>>> > > > > @@ -580,8 +580,6 @@ static int mr75203_probe(struct
>>>>> > > > > platform_device *pdev)
>>>>> > > > >       }
>>>>> > > > >
>>>>> > > > >       if (vm_num) {
>>>>> > > > > -             u32 num = vm_num;
>>>>> > > > > -
>>>>> > > > >               ret = pvt_get_regmap(pdev, "vm", pvt);
>>>>> > > > >               if (ret)
>>>>> > > > >                       return ret;
>>>>> > > > > @@ -594,30 +592,28 @@ static int mr75203_probe(struct
>>>>> > > > > platform_device *pdev)
>>>>> > > > >               ret = device_property_read_u8_array(dev, "intel,vm-map",
>>>>> > > > > pvt->vm_idx, vm_num);
>>>>> > > > >               if (ret) {
>>>>> > > > > -                     num = 0;
>>>>> > > > > +                     /*
>>>>> > > > > +                      * Incase intel,vm-map property is not
>>>>> > > > > defined, we
>>>>> > > > > +                      * assume incremental channel numbers.
>>>>> > > > > +                      */
>>>>> > > > > +                     for (i = 0; i < vm_num; i++)
>>>>> > > > > + pvt->vm_idx[i] = i;
>>>>> > > > >               } else {
>>>>> > > > >                       for (i = 0; i < vm_num; i++)
>>>>> > > > >                               if (pvt->vm_idx[i] >= vm_num ||
>>>>> > > > > - pvt->vm_idx[i] == 0xff) {
>>>>> > > > > - num = i;
>>>>> > > > > + pvt->vm_idx[i] == 0xff)
>>>>> > > > > break;
>>>>> > > >
>>>>> > > > So all vm_idx values from 0x00 to 0xfe would be acceptable ?
>>>>> > > > Does the chip really have that many registers (0x200 + 0x40 +
>>>>> > > > 0x200 * 0xfe) ?
>>>>> > > > Is that documented somewhere ?
>>>>> > > According to the code vm_num is limited to 32 because the mask is
>>>>> > > only 5 bits:
>>>>> > >
>>>>> > > #define VM_NUM_MSK    GENMASK(20, 16)
>>>>> > > #define VM_NUM_SFT    16
>>>>> > > vm_num = (val & VM_NUM_MSK) >> VM_NUM_SFT;
>>>>> > >
>>>>> > > In practice according to the data sheet I have:
>>>>> > > 0 <= VM instances <= 8
>>>>> > >
>>>>> > Sorry, my bad. I misread the patch and thought the first part of
>>>>> > the if statement was removed.
>>>>> >
>>>>> > Anyway, what is the difference between specifying an vm_idx value of
>>>>> > 0xff and not specifying anything ? Or, in other words, taking the dt
>>>>> > example, the difference between
>>>>> >        intel,vm-map = [03 01 04 ff ff];
>>>>> > and
>>>>> >        intel,vm-map = [03 01 04];
>>>>>
>>>>> The actual number of VMs is read from a HW register:
>>>>>     ret = regmap_read(pvt->c_map, PVT_IP_CONFIG, &val);
>>>>>     ...
>>>>>     vm_num = (val & VM_NUM_MSK) >> VM_NUM_SFT;
>>>>>
>>>>> Also, using:
>>>>>     ret = device_property_read_u8_array(dev, "intel,vm-map", vm_idx,
>>>>>                         vm_num);
>>>>> in the driver will fail if vm_num > sizeof array in device-tree.
>>>>>
>>>>> So, if for example vm_num = 5, but you will want to map only 3 of them
>>>>> you most set property to be:
>>>>>     intel,vm-map = [03 01 04 ff ff];
>>>>> otherwise if you set:
>>>>>     intel,vm-map = [03 01 04];
>>>>> it will assume the property doesn't, and will continue the flow in code
>>>>> as if it doesn’t exist (which is not what the user wanted, and before my
>>>>> fix also has a bug).
>>>>
>>>> There should be some error handling to catch this case (ie if the number
>>>> of entries does not match the expected count), or if a value in the array
>>>> is larger or equal to vm_num. Today the latter is silently handled as end
>>>> of entries (similar to 0xff), but that should result in an error.
>>>> This would avoid situations like
>>>>        intel,vm-map = [01 02 03 04 05];
>>>> ie where the person writing the devicetree file accidentally entered
>>>> index values starting with 1 instead of 0. A mismatch between vm_num
>>>> and the number of entries in the array is silently handled as if there
>>>> was no property at all, which is at the very least misleading and
>>>> most definitely unexpected and should also result in an error.
>>>
>>>
>>> I assume it is possible to tell according to the return value, if property
>>> doesn’t exist at all, or if it does exists and size of array in
>>> device-tree is smaller than vm_num.
>>> In [PATCH v3 17/19] Andy wrote that “code shouldn't be a YAML validator.
>>> Drop this and make sure you have correct DT schema” so I’m a bit confused
>>> if code should validate “intel,bm-map” or if it is the user responsibility.
>>> As this property was not added by me, I prefer not to fix it as part of
>>> this series of patches.
>>>
>>
>> You are changing the driver all over the place with 19 patches, including
>> this code, but you don't want to add code that validates the devicetree
>> data ? That seems odd.
>>
> OK. I have added patch #20 to validate that same VM index doesn't appear
> more than once in intel,vm-map.
> 
> u32 vm_mask = 0;
> 
> for (i = 0; i < vm_num; i++) {
>      if (vm_idx[i] >= vm_num || vm_idx[i] == 0xff)

I think "vm_idx[i] >= vm_num && vm_idx[i] != 0xff)
should also be invalid, ie.

	if (vm_idx[i] == 0xff)
		break;
	if (vm_idx[i] >= vm_num)
		return -EINVAL;

Thanks,
Guenter

>          break;
> 
>      if (vm_mask & BIT(vm_idx[i])) {
>          dev_err(dev, "Same VM appears more than once in intel,vm-map\n",
>              vm_idx[i]);
>          return EINVAL;
>      }
> 
>      vm_mask |= BIT(vm_idx[i]);
> }
> 
> 
>>>
>>>> Also, what happens if the devicetree content is something like the
>>>> following ? Would that be valid ?
>>>>        intel,vm-map = [00 01 01 01 01 01];
>>>
>>> If device-tree content would be:
>>>      intel,vm-map = [00 01 01 01 01 01];
>>> and assuming 16 channels for each VM, the hwmon sub-system will expose 90
>>> sysfs to read voltage values.
>>> In practice 16 – 31, 32 – 47, 48 – 63, 64 – 89 will all report the same
>>> input signals for VM1.
>>>
>>
>> Does that make any sense, and is there a valid reason to have a mapping
>> table like the one in this example ?
> 
> I can't find any sense in having such a mapping.
> Anyway the new patch will not allow it to happen.
> 
> -- 
> Regards, Eliav
>