Re: [PATCH 14/17] fpga: dfl: fme: add thermal management support

[Wu Hao]

On Tue, Apr 02, 2019 at 07:59:25AM -0700, Moritz Fischer wrote:
> Hi Wu,
> 
> On Mon, Mar 25, 2019 at 11:07:41AM +0800, Wu Hao wrote:
> > This patch adds support to thermal management private feature for DFL
> > FPGA Management Engine (FME). As thermal throttling is handled by
> > hardware automatically per pre-defined thresholds, this private
> > feature driver only provides read-only sysfs interfaces for user
> > to read temperature, thresholds, threshold policy and other info.
> > 
> > Signed-off-by: Luwei Kang <luwei.kang@xxxxxxxxx>
> > Signed-off-by: Russ Weight <russell.h.weight@xxxxxxxxx>
> > Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxx>
> > Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
> > ---
> >  Documentation/ABI/testing/sysfs-platform-dfl-fme |  56 +++++++
> >  drivers/fpga/dfl-fme-main.c                      | 202 +++++++++++++++++++++++
> >  2 files changed, 258 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-platform-dfl-fme b/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > index b8327e9..d3aeb88 100644
> > --- a/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > +++ b/Documentation/ABI/testing/sysfs-platform-dfl-fme
> > @@ -44,3 +44,59 @@ Description:	Read-only. It returns socket_id to indicate which socket
> >  		this FPGA belongs to, only valid for integrated solution.
> >  		User only needs this information, in case standard numa node
> >  		can't provide correct information.
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/temperature
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. It returns temperature (in Celsius) of this FPGA
> > +		device.
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/threshold1
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. Read this file to get the temperature threshold1
> > +		(in Celsius).
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/threshold2
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. Read this file to get the temperature threshold2
> > +		(in Celsius).
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/trip_threshold
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. It returns trip threshold (in Celsius), once FPGA
> > +		temperature reaches trip threshold, it triggers a fatal event
> > +		to board management controller (BMC) to shutdown FPGA.
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/threshold1_status
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. It returns 1 if temperature reaches threshold1,
> > +		otherwise 0. Once temperature reaches threshold1, hardware
> > +		will automatically enter throttling state (AP1 - 50%
> > +		or AP2 - 90% throttling, see 'threshold1_policy').
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/threshold2_status
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. It returns 1 if temperature reaches threshold2,
> > +		otherwise 0. Once temperature reaches threshold2, hardware
> > +		will automatically enter the deepest throttling state (AP6
> > +		- 100% throttling).
> > +
> > +What:		/sys/bus/platform/devices/dfl-fme.0/thermal_mgmt/threshold1_policy
> > +Date:		March 2019
> > +KernelVersion:  5.2
> > +Contact:	Wu Hao <hao.wu@xxxxxxxxx>
> > +Description:	Read-only. Read this file to get the policy of temperature
> > +		threshold1. It only supports two value (policy):
> > +		    0 - AP2 state (90% throttling)
> > +		    1 - AP1 state (50% throttling)
> 
> These look like they could directly map to the linux thermal framework,
> any reason you can't use the thermal framework?
> 
> The trip stuff literally maps 1:1 to what a thermal driver does, I think
> that's something you'd wanna consider.
> 

Hi Moritz,

Thanks a lot for the suggestion, actually I feel that the trip points in thermal
zone are used to indicate cooling actions required for thermal software either
in kernel or userspace. But in this case, such FPGA hardware handles cooling
automatically (yes, driver only expose Read-only sysfs for information), so
software doesn't need to take care of this at all. For this purpose, it seems
that we don't have to put these thresholds as trip points. And per my
understanding, if people use such FPGA device, then they may need to know
what's the current hardware throttling behavior, e.g. 50% vs 90%. These
information can't be provided by standard thermal zone sysfs, so anyway user
needs these sysfs interfaces to know it. But it seems that we still could
create a thermal zone without trip points, it could help if user wants to
connect some external cooling devices via userspace thermal daemon, they can
define whatever trip points they like to activate the external cooling 
device. I will consider this further more and come up with a new patch in
v2 patchset.

Thanks
Hao

> Cheers,
> Moritz