Re: [PATCH] hwmon: (jc42) Strengthen detect function

[Guenter Roeck <linux@roeck-us.net>]

On 10/14/24 05:12, Jean Delvare wrote:
> Hi Guenter,
> 
> On Sun, 30 Jun 2024 13:20:28 -0700, Guenter Roeck wrote:
>> Configuration register bit 5 must read 0 for all JC42.4 compliant chips.
>> Several capability register bits must be set for all TSE2004 compliant
>> chips. Use that information to strengthen the detect function.
>>
>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> ---
>>   drivers/hwmon/jc42.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/hwmon/jc42.c b/drivers/hwmon/jc42.c
>> index 1180af1b1638..a260cff750a5 100644
>> --- a/drivers/hwmon/jc42.c
>> +++ b/drivers/hwmon/jc42.c
>> @@ -413,7 +413,11 @@ static int jc42_detect(struct i2c_client *client, struct i2c_board_info *info)
>>   	if (cap < 0 || config < 0 || manid < 0 || devid < 0)
>>   		return -ENODEV;
>>   
>> -	if ((cap & 0xff00) || (config & 0xf800))
>> +	if ((cap & 0xff00) || (config & 0xf820))
>> +		return -ENODEV;
>> +
>> +	if ((devid & TSE2004_DEVID_MASK) == TSE2004_DEVID &&
>> +	    (cap & 0x00e7) != 0x00e7)
>>   		return -ENODEV;
>>   
>>   	for (i = 0; i < ARRAY_SIZE(jc42_chips); i++) {
> 
> I have a user reporting that this change is causing the jc42 driver to
> no longer bind to his memory module temperature sensor devices after
> updating to kernel v6.11. I asked for a register dump:
> 
>       0,8  1,9  2,a  3,b  4,c  5,d  6,e  7,f
> 00: 7f00 0000 0000 0000 0000 6ac2 091b 3022
> 
> After swapping the bytes, I see that this is a TSE2004-compliant device
> (devid = 0x2230) and the capabilities register reads 0x007f. This
> doesn't pass the 0x00e7 mask test you added, as bit 7 isn't set in his
> case.
> 
> The JEDEC standard indeed says that bit 7 should be set, but apparently
> this isn't always the case in the real world.
> 
> Also note that I looked at the Renesas TSE2004GB2B0 datasheet and it
> shows bit 2 (RANGE) as not always set. The ST STTS2004 datasheet shows
> bits 0 (EVENT) and 2 (RANGE) as possibly reading 0. So I wonder how
> much we can rely on these capability bits being set in the detect
> function. Unfortunately I don't have any TS2004-compliant device at
> hand to verify, nor do I own register dumps of such devices. Would it
> be OK with you if we relax the check to at least ignore bit 7, and
> possibly also bits 0 and 2?
> 

Sigh. I guess it would have been a miracle if vendors followed the standard.
Let's ignore all three bits, with explanation. Care to send a patch, or do
you want me to do it ?

Thanks,
Guenter