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

[Mike Leach]

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.

Mike

> Let me know if you have any concerns or good suggestions for this solution.
>
>
> Best,
>
> Tao
>
> >
> > Kind regards
> > Suzuki
> >
> >



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK