Re: [PATCH V2 09/15] coresight: tmc: adding mode of operation for link/sinks

[Suzuki K Poulose]

On 19/04/16 16:45, Mathieu Poirier wrote:
> On 19 April 2016 at 07:19, Suzuki K Poulose <Suzuki.Poulose@xxxxxxx> wrote:
> > On 12/04/16 18:54, Mathieu Poirier wrote:
> > > Moving tmc_drvdata::enable to a local_t mode.  That way the
> > > sink interface is aware of it's orgin and the foundation for
> > > mutual exclusion between the sysFS and Perf interface can be
> > > laid out.
> > >
> > > Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > > ---
> > >    drivers/hwtracing/coresight/coresight-tmc-etf.c | 28
> > > ++++++++++++++++++-------
> > >    drivers/hwtracing/coresight/coresight-tmc-etr.c | 24
> > > ++++++++++++++++-----
> > >    drivers/hwtracing/coresight/coresight-tmc.h     |  4 ++--
> > >    3 files changed, 42 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > > b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > > index 7cb287ef7b9e..5908000e1ae0 100644
> > > --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > > +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > > @@ -110,6 +110,7 @@ static int tmc_enable_etf_sink(struct coresight_device
> > > *csdev, u32 mode)
> > >    {
> > >          bool allocated = false;
> > >          char *buf = NULL;
> > > +       u32 val;
> > >          unsigned long flags;
> > >          struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> > >
> > > @@ -146,6 +147,15 @@ fast_path:
> > >                  return -EBUSY;
> > >          }
> > >
> > > +       val = local_xchg(&drvdata->mode, mode);
> > > +       /*
> > > +        * In sysFS mode we can have multiple writers per sink.  Since
> > > this
> > > +        * sink is already enabled no memory is needed and the HW need not
> > > be
> > > +        * touched.
> > > +        */
> > > +       if (val == CS_MODE_SYSFS)
> > > +               goto out;
> > > +
> >
> >
> > We are not dropping the spinlock in this case. Are we ?
>
> Definitely - thanks for pointing that out.
>
> > > diff --git a/drivers/hwtracing/coresight/coresight-tmc.h
> > > b/drivers/hwtracing/coresight/coresight-tmc.h
> > > index 80096fa75326..821bdf150ac9 100644
> > > --- a/drivers/hwtracing/coresight/coresight-tmc.h
> > > +++ b/drivers/hwtracing/coresight/coresight-tmc.h
> > > @@ -100,7 +100,7 @@ enum tmc_mem_intf_width {
> > >     * @paddr:    DMA start location in RAM.
> > >     * @vaddr:    virtual representation of @paddr.
> > >     * @size:     @buf size.
> > > - * @enable:    this TMC is being used.
> > > + * @mode:      how this TMC is being used.
> > >     * @config_type: TMC variant, must be of type @tmc_config_type.
> > >     * @trigger_cntr: amount of words to store after a trigger.
> > >     */
> > > @@ -116,7 +116,7 @@ struct tmc_drvdata {
> > >          dma_addr_t              paddr;
> > >          void __iomem            *vaddr;
> > >          u32                     size;
> > > -       bool                    enable;
> > > +       local_t                 mode;
> >
> >
> > Since we always deal with the mode under the spinlock, do we really need
> > this to
> > be local_t ? Or do we plan to get rid of the lock ?
>
> You are correct, using a local_t variable isn't strictly needed here.  But:
>
> 1) It greatly simplifies the code.

+1

> 2) I'm really hoping one day we can do without the spinlocks, though I
> don't know when that will happen.
>
> Get back to me if you're resolute on switching the local_t to a normal type.

No, leave it as it is, as you said, it does simplify the code.