linux-kernel - Re: [PATCH] hwmon: (pmbus/lm25066) Swap low/high current coefficients for LM5066(i)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <91322e5e-23e3-ea6a-04bd-1c23fedadbf7@roeck-us.net>
Date:   Wed, 22 Nov 2017 17:17:44 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Rob Lippert <rlippert@...gle.com>
Cc:     Robert Lippert <roblip@...il.com>, linux-hwmon@...r.kernel.org,
        jdelvare@...e.com, linux-kernel@...r.kernel.org,
        Xo Wang <xow@...gle.com>
Subject: Re: [PATCH] hwmon: (pmbus/lm25066) Swap low/high current coefficients
 for LM5066(i)

Hi Rob,

On 11/22/2017 03:39 PM, Rob Lippert wrote:
> On Wed, Nov 22, 2017 at 3:28 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On Wed, Nov 22, 2017 at 02:07:28PM -0800, Robert Lippert wrote:
>>> The _L low-current mode coefficient values should reference the
>>> datasheet rows with CL=VDD but it seems were mistakenly pulled from
>>> the rows with CL=GND.
>>>
>>> This causes the current/power to be reported as approximately double
>>> the actual value when CL=GND and half the actual value when CL=VDD.
>>>
>>
>> This would affect all chips supported by this driver. Hmm, and I was sure
>> I tested this. I'll have to dig out my hardware and confirm.
> 
> I'm still not 100% convinced this commit is correct as I haven't been
> able to validate the measurements against an external probe yet (and
> my test board uses a non-standard sense resistor which means it needs
> additional massaging of the data anyhow).
> 
>>
>>
>> The code currently only uses bit 4 of the DEVICE_SETUP (D9h) command
>> to determine which current limit setting to use. Looking into the
>> datasheet, it looks like it also has to evaluate bit 2, and I wonder
>> if there is a means to determine CL if bit 2 = 0. Any idea ?
> 
> On my test board CL=floating (equivalent to GND) and the value of
> register 0xD9 is all zeroes.
> 
Are you sure that floating is equivalent to GND ? I didn't check the
datasheet, but it is more common for chips to have an internal pull-up.

>>
>> Does bit 4 report the CL pin value if bit 2 = 0 ?
> 
> I can't tell by reading the datasheet that 0xD9 bit4 will ever report
> the pin value as the language is difficult to parse :)

Same here.

> But I don't have any hardware setup with CL=VDD to test...
> 

I do have various evaluation boards, so I should be able to do some testing.
I hope I'll get to it over the weekend.

Guenter