From: Guenter Roeck <linux@roeck-us.net>
To: Lars Petter Mostad <larspm@gmail.com>
Cc: jdelvare@suse.com, linux-hwmon@vger.kernel.org,
Lars Petter Mostad <lars.petter.mostad@appear.net>
Subject: Re: [PATCH] hwmon: (emc1403) Decode fractional temperatures.
Date: Tue, 30 Apr 2024 08:37:20 -0700 [thread overview]
Message-ID: <372d0822-2aff-4663-998a-31cd1db4ab4b@roeck-us.net> (raw)
In-Reply-To: <CAC-Dm243rwTcRS2_p989yUoFUjDoR4p9NGE-8WwwmaA6=Ko+4w@mail.gmail.com>
On 4/30/24 04:11, Lars Petter Mostad wrote:
> On Sun, Apr 28, 2024 at 8:07 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> On Sun, Apr 28, 2024 at 11:00:47AM -0700, Guenter Roeck wrote:
>>> On Fri, Apr 26, 2024 at 04:13:22PM +0200, Lars Petter Mostad wrote:
>>>> Decode all diode data low byte registers.
>>>>
>>> All ?
>
>>> What about the following ?
>>>
>>> 2c -> 2e
>>> 2d -> 2f
>>
>> Also all other limit registers, and for those the write part is missing.
>
> Yes, my intention was only to decode the (already non-zero) data registers,
> not the limit registers.
>
We should really do all or nothing.
>>>> - unsigned int val;
>>>> + unsigned int val, val_lowbyte;
>>>
>>> FWIW, this is wrong. The upper bit of the high byte is a sign bit
>>> on emc1438.
>
> Yes, I missed the sign bit in the datasheets. See my comment on patch for
> emc1438. If I withdraw the EMC1438 patch, this will work for the current
> chips with unsigned registers.
>
Adding support for the new chip is desirable. Please don't drop it.
>>> retval = regmap_read(data->regmap, sda->index, &val);
>>> if (retval < 0)
>>> return retval;
>>> - return sprintf(buf, "%d000\n", val);
>>> +
>>> + if (idx_lowbyte) {
>>> + retval = regmap_read(data->regmap, idx_lowbyte, &val_lowbyte);
>>> + if (retval < 0)
>>> + val_lowbyte = 0;
>>
>> This is an error and should be handled, not ignored.
>
> My idea here was that if for some reason it manages to read the high byte but
> not the low byte, I don't break anything. The output will be the same as before
> the patch.
>
No, you should handle the error.
>>> + return sprintf(buf, "%d\n",
>>> + (((val << 8) | val_lowbyte) * (u32)1000) >> 8);
>>
>> The u32 typecast is unnecessary and would interfer with negative temperatures.
>
> I put the u32 typecast there on the off chance that somebody will compile
> this with a compiler with 16-bit ints (uClinux?), as C only guarantees 16 bits
> for unsigned int. It would of course have to change if negative values are
> to be supported.
I don't even know if such a system exists, but if it does it won't build a Linux
kernel. It doesn't make sense to even try to support a system with 16-bit integers.
>
> Is it acceptable to handle the low byte for data registers only?
>
No, as mentioned above.
> Should it be kept unsigned only (if dropping emc1438 patch)?
>
You should not drop the emc1438 patch. What I would suggest, though,
is to consider converting the driver to use the _with_info registration
API. That would simplify the code a lot and make it much easier to add
support for new chips and to add conditional support for signed temperatures.
Thanks,
Guenter
prev parent reply other threads:[~2024-04-30 15:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 14:13 [PATCH] hwmon: (emc1403) Decode fractional temperatures Lars Petter Mostad
2024-04-28 18:00 ` Guenter Roeck
2024-04-28 18:07 ` Guenter Roeck
2024-04-30 11:11 ` Lars Petter Mostad
2024-04-30 15:37 ` Guenter Roeck [this message]
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