linux-kernel - Re: [PATCH v3 04/12] fpga: dfl: afu: add AFU state related sysfs interfaces

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Message-ID: <20190724132920.GB8463@hao-dev>
Date:   Wed, 24 Jul 2019 21:29:20 +0800
From:   Wu Hao <hao.wu@...el.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, atull@...nel.org,
        Ananda Ravuri <ananda.ravuri@...el.com>,
        Xu Yilun <yilun.xu@...el.com>
Subject: Re: [PATCH v3 04/12] fpga: dfl: afu: add AFU state related sysfs
 interfaces

On Wed, Jul 24, 2019 at 11:41:10AM +0200, Greg KH wrote:
> On Tue, Jul 23, 2019 at 12:51:27PM +0800, Wu Hao wrote:
> > This patch introduces more sysfs interfaces for Accelerated
> > Function Unit (AFU). These interfaces allow users to read
> > current AFU Power State (APx), read / clear AFU Power (APx)
> > events which are sticky to identify transient APx state,
> > and manage AFU's LTR (latency tolerance reporting).
> > 
> > Signed-off-by: Ananda Ravuri <ananda.ravuri@...el.com>
> > Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> > Signed-off-by: Wu Hao <hao.wu@...el.com>
> > Acked-by: Alan Tull <atull@...nel.org>
> > Signed-off-by: Moritz Fischer <mdf@...nel.org>
> > ---
> > v2: rebased, and remove DRV/MODULE_VERSION modifications
> > v3: update kernel version and date in sysfs doc
> > ---
> >  Documentation/ABI/testing/sysfs-platform-dfl-port |  30 +++++
> >  drivers/fpga/dfl-afu-main.c                       | 137 ++++++++++++++++++++++
> >  drivers/fpga/dfl.h                                |  11 ++
> >  3 files changed, 178 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-platform-dfl-port b/Documentation/ABI/testing/sysfs-platform-dfl-port
> > index 6a92dda..5961fb2 100644
> > --- a/Documentation/ABI/testing/sysfs-platform-dfl-port
> > +++ b/Documentation/ABI/testing/sysfs-platform-dfl-port
> > @@ -14,3 +14,33 @@ Description:	Read-only. User can program different PR bitstreams to FPGA
> >  		Accelerator Function Unit (AFU) for different functions. It
> >  		returns uuid which could be used to identify which PR bitstream
> >  		is programmed in this AFU.
> > +
> > +What:		/sys/bus/platform/devices/dfl-port.0/power_state
> > +Date:		July 2019
> > +KernelVersion:	5.4
> > +Contact:	Wu Hao <hao.wu@...el.com>
> > +Description:	Read-only. It reports the APx (AFU Power) state, different APx
> > +		means different throttling level. When reading this file, it
> > +		returns "0" - Normal / "1" - AP1 / "2" - AP2 / "6" - AP6.
> > +
> > +What:		/sys/bus/platform/devices/dfl-port.0/ap1_event
> > +Date:		July 2019
> > +KernelVersion:	5.4
> > +Contact:	Wu Hao <hao.wu@...el.com>
> > +Description:	Read-write. Read or set 1 to clear AP1 (AFU Power State 1)
> > +		event. It's used to indicate transient AP1 state.
> 
> So reading the value changes the state of the system?  That's almost
> always never a good idea.
> 
> Force userspace to write the value to change something.  Otherwise all
> libraries that use sysfs will be accidentally changing the state of your
> system without you ever knowing it.

Oh.. I think the description makes some misunderstanding here, will fix it
in the next version. This AP1/AP2 event will only be cleared by write 1 to
it, read will not change the state.

> 
> > +
> > +What:		/sys/bus/platform/devices/dfl-port.0/ap2_event
> > +Date:		July 2019
> > +KernelVersion:	5.4
> > +Contact:	Wu Hao <hao.wu@...el.com>
> > +Description:	Read-write. Read or set 1 to clear AP2 (AFU Power State 2)
> > +		event. It's used to indicate transient AP2 state.
> > +
> > +What:		/sys/bus/platform/devices/dfl-port.0/ltr
> > +Date:		July 2019
> > +KernelVersion:	5.4
> > +Contact:	Wu Hao <hao.wu@...el.com>
> > +Description:	Read-write. Read and set AFU latency tolerance reporting value.
> > +		Set ltr to 1 if the AFU can tolerate latency >= 40us or set it
> > +		to 0 if it is latency sensitive.
> > diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
> > index 68b4d08..cb3f73e 100644
> > --- a/drivers/fpga/dfl-afu-main.c
> > +++ b/drivers/fpga/dfl-afu-main.c
> > @@ -141,8 +141,145 @@ static int port_get_id(struct platform_device *pdev)
> >  }
> >  static DEVICE_ATTR_RO(id);
> >  
> > +static ssize_t
> > +ltr_show(struct device *dev, struct device_attribute *attr, char *buf)
> > +{
> > +	struct dfl_feature_platform_data *pdata = dev_get_platdata(dev);
> > +	void __iomem *base;
> > +	u64 v;
> > +
> > +	base = dfl_get_feature_ioaddr_by_id(dev, PORT_FEATURE_ID_HEADER);
> > +
> > +	mutex_lock(&pdata->lock);
> > +	v = readq(base + PORT_HDR_CTRL);
> > +	mutex_unlock(&pdata->lock);
> 
> Why do you need a lock to call readq()?  What are you protecting here?

If this code is running on 32bit machine, readq will be replaced with 2
readl operation. If that is the case, should we protect the code against
it?

> 
> 
> > +
> > +	return sprintf(buf, "%x\n", (u8)FIELD_GET(PORT_CTRL_LATENCY, v));
> > +}
> > +
> > +static ssize_t
> > +ltr_store(struct device *dev, struct device_attribute *attr,
> > +	  const char *buf, size_t count)
> > +{
> > +	struct dfl_feature_platform_data *pdata = dev_get_platdata(dev);
> > +	void __iomem *base;
> > +	u8 ltr;
> > +	u64 v;
> > +
> > +	if (kstrtou8(buf, 0, &ltr) || ltr > 1)
> > +		return -EINVAL;
> 
> Are you doing anything with this value?  If not, how about just using
> the sysfs boolean read function and if it is 1, then do the clearing?
> 
> Same for all other show/store functions in here.

Sure, will fix this in the next version.

Thanks a lot for the comments.

Hao

> 
> thanks,
> 
> greg k-h