Re: [PATCH v5 1/6] misc: Add Synopsys DesignWare xData IP driver

Greg Kroah-Hartman
2021-02-11T10:03:56Z

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?

thanks,

greg k-h