Re: [PATCH v4 07/11] coresight-tpdm: Add nodes for dsb edge control

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 02/06/2023 09:45, Suzuki K Poulose wrote:
> On 02/06/2023 09:21, Tao Zhang wrote:
>>
>> On 6/1/2023 8:14 PM, Suzuki K Poulose wrote:
>>> On 27/04/2023 10:00, 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@quicinc.com>
>>>> ---
>>>>   .../ABI/testing/sysfs-bus-coresight-devices-tpdm   |  32 +++++
>>>>   drivers/hwtracing/coresight/coresight-tpdm.c       | 135 
>>>> ++++++++++++++++++++-
>>>>   drivers/hwtracing/coresight/coresight-tpdm.h       |  21 ++++
>>>>   3 files changed, 187 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git 
>>>> a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm 
>>>> b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpdm
>>>> index 348e167..a57f000 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    6.3
>>>> +Contact:    Jinlong Mao (QUIC) <quic_jinlmao@quicinc.com>, Tao 
>>>> Zhang (QUIC) <quic_taozha@quicinc.com>
>>>> +Description:
>>>> +        Read/Write a set of the edge control registers of the DSB
>>>> +        in TPDM.
>>>> +
>>>> +        Expected format is the following:
>>>> +        <integer1> <integer2> <integer3>
>>>> +
>>>> +        Where:
>>>> +        <integer1> : Start EDCR register number
>>>> +        <integer2> : End EDCR register number
>>>> +        <integer3> : The value need to be written
>>>> +
>>>> +What: /sys/bus/coresight/devices/<tpdm-name>/dsb_edge_ctrl_mask
>>>> +Date:        March 2023
>>>> +KernelVersion    6.3
>>>> +Contact:    Jinlong Mao (QUIC) <quic_jinlmao@quicinc.com>, Tao 
>>>> Zhang (QUIC) <quic_taozha@quicinc.com>
>>>> +Description:
>>>> +        Read/Write a set of the edge control mask registers of the
>>>> +        DSB in TPDM.
>>>> +
>>>> +        Expected format is the following:
>>>> +        <integer1> <integer2> <integer3>
>>>> +
>>>> +        Where:
>>>> +        <integer1> : Start EDCMR register number
>>>> +        <integer2> : End EDCMR register number
>>>> +        <integer3> : The value need to be written
>>>> diff --git a/drivers/hwtracing/coresight/coresight-tpdm.c 
>>>> b/drivers/hwtracing/coresight/coresight-tpdm.c
>>>> index 1bacaa5..a40e458 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-tpdm.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-tpdm.c
>>>> @@ -80,7 +80,14 @@ static void set_trigger_type(struct tpdm_drvdata 
>>>> *drvdata, u32 *val)
>>>>     static void tpdm_enable_dsb(struct tpdm_drvdata *drvdata)
>>>>   {
>>>> -    u32 val;
>>>> +    u32 val, i;
>>>> +
>>>> +    for (i = 0; i < TPDM_DSB_MAX_EDCR; i++)
>>>> +        writel_relaxed(drvdata->dsb->edge_ctrl[i],
>>>> +               drvdata->base + TPDM_DSB_EDCR(i));
>>>> +    for (i = 0; i < TPDM_DSB_MAX_EDCMR; i++)
>>>> +        writel_relaxed(drvdata->dsb->edge_ctrl_mask[i],
>>>> +               drvdata->base + TPDM_DSB_EDCMR(i));
>>>
>>> Do all TPDM DSBs have MAX_EDCR registers ? Or some have less than that ?
>>> If it is latter, do we need special care to avoid writing to inexistent
>>> registers ?
>>>
>> You are right, not all DSB TPDMs have MAX_EDCR registers. In our 
>> design, the inexistent register addresses
>>
>> are not occupied and safe for accessing.

Does the TRM for the component say so ? Or is it by luck ? If the spec
says it is RAZ/WriteIgnore, then we could keep the code as it is,
with a comment. Otherwise, we could add a DT property. So please get
this clarified with the H/W designers.

Suzuki