Re: [PATCH v6 09/13] Add nodes for dsb edge control

[Suzuki K Poulose]

On 13/07/2023 09:54, Mike Leach wrote:
> HI Tao,
>
> On Wed, 12 Jul 2023 at 14:53, Tao Zhang <quic_taozha@xxxxxxxxxxx> wrote:
> > On 6/20/2023 9:41 PM, Suzuki K Poulose wrote:
> > > On 20/06/2023 09:31, Tao Zhang wrote:
> > > > On 6/20/2023 3:37 PM, Greg Kroah-Hartman wrote:
> > > > > On Tue, Jun 20, 2023 at 03:32:37PM +0800, Tao Zhang wrote:
> > > > > > Add the nodes to set value for DSB edge control and DSB edge
> > > > > > control mask. Each DSB subunit TPDM has maximum of n(n<16) EDCR
> > > > > > resgisters to configure edge control. DSB edge detection control
> > > > > > 00: Rising edge detection
> > > > > > 01: Falling edge detection
> > > > > > 10: Rising and falling edge detection (toggle detection)
> > > > > > And each DSB subunit TPDM has maximum of m(m<8) ECDMR registers to
> > > > > > configure mask. Eight 32 bit registers providing DSB interface
> > > > > > edge detection mask control.
> > > > > >
> > > > > > Signed-off-by: Tao Zhang <quic_taozha@xxxxxxxxxxx>
> > > > > > ---
> > > > > >    .../ABI/testing/sysfs-bus-coresight-devices-tpdm   |  32 +++++
> > > > > >    drivers/hwtracing/coresight/coresight-tpdm.c       | 143
> > > > > > ++++++++++++++++++++-
> > > > > >    drivers/hwtracing/coresight/coresight-tpdm.h       |  22 ++++
> > > > > >    3 files changed, 196 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git
> > > > > > a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > > > > b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > > > > index 2a82cd0..34189e4a 100644
> > > > > > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > > > > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
> > > > > > @@ -60,3 +60,35 @@ Description:
> > > > > >            Bit[3] : Set to 0 for low performance mode.
> > > > > >                     Set to 1 for high performance mode.
> > > > > >            Bit[4:8] : Select byte lane for high performance mode.
> > > > > > +
> > > > > > +What: /sys/bus/coresight/devices/<tpdm-name>/dsb_edge_ctrl
> > > > > > +Date:        March 2023
> > > > > > +KernelVersion    6.5
> > > > > > +Contact:    Jinlong Mao (QUIC) <quic_jinlmao@xxxxxxxxxxx>, Tao
> > > > > > Zhang (QUIC) <quic_taozha@xxxxxxxxxxx>
> > > > > > +Description:
> > > > > > +        Read/Write a set of the edge control registers of the DSB
> > > > > > +        in TPDM.
> > > > > > +
> > > > > > +        Expected format is the following:
> > > > > > +        <integer1> <integer2> <integer3>
> > > > > sysfs is "one value", not 3.  Please never have to parse a sysfs file.
> > > >
> > > > Do you mean sysfs file can only accept "one value"?
> > > >
> > > > I see that more than one value are written to the sysfs file
> > > > "trigout_attach".
> > > >
> > > > > > +static ssize_t dsb_edge_ctrl_show(struct device *dev,
> > > > > > +                       struct device_attribute *attr,
> > > > > > +                       char *buf)
> > > > > > +{
> > > > > > +    struct tpdm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > > > > > +    ssize_t size = 0;
> > > > > > +    unsigned long bytes;
> > > > > > +    int i;
> > > > > > +
> > > > > > +    spin_lock(&drvdata->spinlock);
> > > > > > +    for (i = 0; i < TPDM_DSB_MAX_EDCR; i++) {
> > > > > > +        bytes = sysfs_emit_at(buf, size,
> > > > > > +                  "Index:0x%x Val:0x%x\n", i,
> > > > > Again, no, one value, no "string" needed to parse anything.
> > > >
> > > > I also see other sysfs files can be read more than one value in other
> > > > drivers.
> > > >
> > > > Is this "one value" limitation the usage rule of Linux sysfs system?
> > > >
> > > > Or am I misunderstanding what you mean?
> > >
> > > Please fix the other sysfs tunables in the following patches.
> >
> > List a new solution for the similar cases below, please see if this
> > design is reasonable?
> >
> > 1. Two SysFS files("dsb_edge_ctrl_idx" and "dsb_edge_ctrl_val") will be
> > created in this case.
> >
> > 2. First write to the node "dsb_edge_ctrl_idx" to set the index number
> > of the edge detection.
> >
> > 3. Then write to the node "dsb_edge_ctrl_val" to set the value of the
> > edge detection.
> >
> > For example, if we need need to set "Falling edge detection" to the edge
> > detection #220-#222, we can issue the following commands.
> >
> > echo 0xdc > tpdm1/dsb_edge_ctrl_idx
> >
> > echo 0x1 > tpdm1/dsb_edge_ctrl_val
> >
> > echo 0xdd > tpdm1/dsb_edge_ctrl_idx
> >
> > echo 0x1 > tpdm1/dsb_edge_ctrl_val
> >
> > echo 0xde > tpdm1/dsb_edge_ctrl_idx
> >
> > echo 0x1 > tpdm1/dsb_edge_ctrl_val
> >
> > If this design is acceptable, we will rewrite other similar nodes based
> > on this solution.
>
> This index / value model is used in the coresight drivers so should be
> OK - eg etm4 has cntr_idx / cntrldvr / cntr_val / cntr_ctrl, where
> index selects the counter, and the other val registers are applied to
> that counter.

True. That model is useful when there are variable number of "counters".
I guess it doesn't hurt to have a 64bit (or even 32bit) file for each
EDCR.

e.g, edcr0...edcr15

Given there are only 16 of them, it is fine to keep a file for each.
This may be grouped under "mgmt" similar to what we have for other
components. That way, it can be easily hidden by checking for the
presence of DSB.

Suzuki