netdev - RE: [PATCH net-next 3/3] mlxsw: core: Add support for negative temperature readout

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Message-ID: <AM6PR05MB52242201CFF6AF2D037ABDABA2E10@AM6PR05MB5224.eurprd05.prod.outlook.com>
Date:   Sun, 23 Jun 2019 16:34:46 +0000
From:   Vadim Pasternak <vadimp@...lanox.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>, mlxsw <mlxsw@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>
Subject: RE: [PATCH net-next 3/3] mlxsw: core: Add support for negative
 temperature readout



> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: Sunday, June 23, 2019 7:26 PM
> To: Vadim Pasternak <vadimp@...lanox.com>
> Cc: Ido Schimmel <idosch@...sch.org>; netdev@...r.kernel.org;
> davem@...emloft.net; Jiri Pirko <jiri@...lanox.com>; mlxsw
> <mlxsw@...lanox.com>; Ido Schimmel <idosch@...lanox.com>
> Subject: Re: [PATCH net-next 3/3] mlxsw: core: Add support for negative
> temperature readout
> 
> > > Why the > 0?
> >
> > We don't consider negative temperature for thermal control.
> 
> Is this because the thermal control is also broken and does not support negative
> values? This is just a workaround papering over the cracks?

We just have system hardware requirements for minimal speed for system
PWM. It could not be less than 20%.
So for temperature ~40C or below it PWM will set to this speed.

> 
> I've worked on some systems where the thermal subsystem has controller a
> heater. Mostly industrial systems, extended temperature range, and you have to
> make sure the hardware is kept above -25C, otherwise the DRAM timing goes to
> pot and the system crashed and froze.

Interesting input. I didn't know about such feature.
We don't have heaters within our systems.
Maybe we should think about it for the next generatin systems.

> 
> 	Andrew