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Date:   Wed, 31 Aug 2022 04:48:40 -0700
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From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v3 02/19] hwmon: (mr75203) fix VM sensor allocation when
 "intel, vm-map" not defined
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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];

Thanks,
Guenter