linux-pci.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Gustavo Pimentel <Gustavo.Pimentel@synopsys.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Derek Kiernan <derek.kiernan@xilinx.com>,
	Dragan Cvetic <dragan.cvetic@xilinx.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Bjorn Helgaas <bhelgaas@google.com>
Subject: RE: [PATCH v5 1/6] misc: Add Synopsys DesignWare xData IP driver
Date: Thu, 11 Feb 2021 10:21:07 +0000	[thread overview]
Message-ID: <DM5PR12MB1835522220E35874106BB924DA8C9@DM5PR12MB1835.namprd12.prod.outlook.com> (raw)
In-Reply-To: <YCT//nmQpOJD9row@kroah.com>

On Thu, Feb 11, 2021 at 9:59:26, Greg Kroah-Hartman 
<gregkh@linuxfoundation.org> wrote:

> On Thu, Feb 11, 2021 at 09:50:33AM +0000, Gustavo Pimentel wrote:
> > On Thu, Feb 11, 2021 at 9:30:16, Greg Kroah-Hartman 
> > <gregkh@linuxfoundation.org> wrote:
> > 
> > > On Thu, Feb 11, 2021 at 10:08:38AM +0100, Gustavo Pimentel wrote:
> > > > +static ssize_t write_show(struct device *dev, struct device_attribute *attr,
> > > > +			  char *buf)
> > > > +{
> > > > +	struct pci_dev *pdev = to_pci_dev(dev);
> > > > +	struct dw_xdata *dw = pci_get_drvdata(pdev);
> > > > +	u64 rate;
> > > > +
> > > > +	mutex_lock(&dw->mutex);
> > > > +	dw_xdata_perf(dw, &rate, true);
> > > > +	mutex_unlock(&dw->mutex);
> > > > +
> > > > +	return sysfs_emit(buf, "%llu MB/s\n", rate);
> > > 
> > > Do not put units in a sysfs file, that should be in the documentation,
> > > otherwise this forces userspace to "parse" the units which is a mess.
> > 
> > Okay.
> > 
> > > 
> > > Same for the other sysfs file.
> > > 
> > > And why do you need a lock for this show function?
> > 
> > Maybe I understood it wrongly, please correct me in that case. The 
> > dw_xdata_perf() is called on the write_show() and read_show(), to avoid a 
> > possible race condition between those calls, I have added this mutex.
> 
> What race?  If the value changes with a write right after a read, what
> does it matter?
> 
> What exactly are you trying to protect with this lock?

The write_store() does a procedure to enable the traffic on the write 
direction, however, the write_show() does a different procedure to 
calculate the link throughput speed, which uses a different set of 
registers on the HW.

Similar happens on the read_store() (which enable the traffic on the read 
direction) and on the read_show()

To summarize write_store() follows the same approach of read_store() and 
the write_show() of the read_show(). I added the mutex on those functions 
for instance to avoid while during the write_show() call the possibility 
of been called the read_show() messing up the link throughput speed 
calculation.
Or while during the write_store() call to be called the read_store or 
even the write_show() for the same reasons.

This is the reason why I added those mutexes, maybe this isn't necessary 
and it's overkill. Please advise me if a different approach can be done.

-Gustavo

> 
> thanks,
> 
> greg k-h



  reply	other threads:[~2021-02-11 10:24 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-11  9:08 [PATCH v5 0/6] misc: Add " Gustavo Pimentel
2021-02-11  9:08 ` [PATCH v5 1/6] misc: " Gustavo Pimentel
2021-02-11  9:30   ` Greg Kroah-Hartman
2021-02-11  9:50     ` Gustavo Pimentel
2021-02-11  9:59       ` Greg Kroah-Hartman
2021-02-11 10:21         ` Gustavo Pimentel [this message]
2021-02-11 10:33           ` Greg Kroah-Hartman
2021-02-11 10:51             ` Gustavo Pimentel
2021-02-11 11:42   ` Leon Romanovsky
2021-02-11 12:32     ` Greg Kroah-Hartman
2021-02-11 13:50       ` Leon Romanovsky
2021-02-11 14:02         ` Greg Kroah-Hartman
2021-02-11 14:13           ` Leon Romanovsky
2021-02-11  9:08 ` [PATCH v5 2/6] misc: Add Synopsys DesignWare xData IP driver to Makefile Gustavo Pimentel
2021-02-11  9:28   ` Greg Kroah-Hartman
2021-02-11  9:40     ` Gustavo Pimentel
2021-02-11  9:08 ` [PATCH v5 3/6] misc: Add Synopsys DesignWare xData IP driver to Kconfig Gustavo Pimentel
2021-02-11 11:29   ` Krzysztof Wilczyński
2021-02-11 13:33     ` Gustavo Pimentel
2021-02-11  9:08 ` [PATCH v5 4/6] Documentation: misc-devices: Add Documentation for dw-xdata-pcie driver Gustavo Pimentel
2021-02-11  9:08 ` [PATCH v5 5/6] MAINTAINERS: Add Synopsys xData IP driver maintainer Gustavo Pimentel
2021-02-11  9:08 ` [PATCH v5 6/6] docs: ABI: Add sysfs documentation interface of dw-xdata-pcie driver Gustavo Pimentel
2021-02-11  9:29   ` Leon Romanovsky
2021-02-11  9:36     ` Greg Kroah-Hartman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=DM5PR12MB1835522220E35874106BB924DA8C9@DM5PR12MB1835.namprd12.prod.outlook.com \
    --to=gustavo.pimentel@synopsys.com \
    --cc=akpm@linux-foundation.org \
    --cc=arnd@arndb.de \
    --cc=bhelgaas@google.com \
    --cc=corbet@lwn.net \
    --cc=derek.kiernan@xilinx.com \
    --cc=dragan.cvetic@xilinx.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --subject='RE: [PATCH v5 1/6] misc: Add Synopsys DesignWare xData IP driver' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).