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

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Message-ID: <e82385f1-de55-4c70-5c5c-35b93a5b2488@arm.com>
Date:   Tue, 20 Jun 2023 14:41:08 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Tao Zhang <quic_taozha@...cinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Konrad Dybcio <konradybcio@...il.com>,
        Mike Leach <mike.leach@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jinlong Mao <quic_jinlmao@...cinc.com>,
        Leo Yan <leo.yan@...aro.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Hao Zhang <quic_hazha@...cinc.com>,
        linux-arm-msm@...r.kernel.org, andersson@...nel.org
Subject: Re: [PATCH v6 09/13] Add nodes for dsb edge control

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@...cinc.com>
>>> ---
>>>   .../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@...cinc.com>, Tao Zhang 
>>> (QUIC) <quic_taozha@...cinc.com>
>>> +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.

Kind regards
Suzuki