linux-kernel - Re: [PATCH v6 4/4] coresight: tpda: add sysfs node to flush specific port

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Message-ID: <dcc1adba-9e7a-4820-8fab-eed14f3d8770@arm.com>
Date: Tue, 23 Dec 2025 09:37:27 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Jie Gan <jie.gan@....qualcomm.com>, Mike Leach <mike.leach@...aro.org>,
 James Clark <james.clark@...aro.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Tingwei Zhang <tingwei.zhang@....qualcomm.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Tao Zhang <tao.zhang@....qualcomm.com>
Subject: Re: [PATCH v6 4/4] coresight: tpda: add sysfs node to flush specific
 port

On 23/12/2025 02:16, Jie Gan wrote:
> 
> 
> On 12/22/2025 9:12 PM, Suzuki K Poulose wrote:
>> On 22/12/2025 06:02, Jie Gan wrote:
>>> From: Tao Zhang <tao.zhang@....qualcomm.com>
>>>
>>> Setting bit i in the TPDA_FLUSH_CR register initiates a flush request
>>> for port i, forcing the data to synchronize and be transmitted to the
>>> sink device.
>>>
>>> Signed-off-by: Tao Zhang <tao.zhang@....qualcomm.com>
>>> Reviewed-by: James Clark <james.clark@...aro.org>
>>> Co-developed-by: Jie Gan <jie.gan@....qualcomm.com>
>>> Signed-off-by: Jie Gan <jie.gan@....qualcomm.com>
>>> ---
>>>   .../ABI/testing/sysfs-bus-coresight-devices-tpda   |  7 ++++
>>>   drivers/hwtracing/coresight/coresight-tpda.c       | 40 +++++++++++ 
>>> + ++++++++++
>>>   drivers/hwtracing/coresight/coresight-tpda.h       |  1 +
>>>   3 files changed, 48 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices- 
>>> tpda b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpda
>>> index d359d90dca72..df8f03d4b573 100644
>>> --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpda
>>> +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tpda
>>> @@ -51,3 +51,10 @@ Description:
>>>           mode 0 - COUNT[11:0] value represents the approximate 
>>> number of bytes moved between two ASYNC packet requests
>>>           mode 1 - the bits COUNT[11:7] are used as a power of 2. for 
>>> example, we could insert an async packet every 8K
>>>                    data by writing a value 13 to the COUNT[11:7] field.
>>> +
>>> +What:        /sys/bus/coresight/devices/<tpda-name>/port_flush_req
>>> +Date:        December 2025
>>> +KernelVersion:    6.19
>>> +Contact:    Jinlong Mao <jinlong.mao@....qualcomm.com>, Tao Zhang 
>>> <tao.zhang@....qualcomm.com>, Jie Gan <jie.gan@....qualcomm.com>
>>> +Description:
>>> +        (RW) Configure the bit i to requests a flush operation of 
>>> port i on the TPDA.
>>
>> Does this have similar semantics as the "global_flush_req"  for "Read" ? 
> 
> Yes, global_flush_req triggers all ports at once, whereas this node 
> initiates a flush request for specific port(s).
> 
> For reading, we can check whether the flush request has completed.

Please document it as such.

Suzuki


> 
> Thanks,
> Jie
> 
>> i.e., the bit stays set until the request completes ? Otherwise, why 
>> isn't this Write only ?
>>
>> I don't see the point of "Reading" this value back.
>>
>> Suzuki
>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-tpda.c b/drivers/ 
>>> hwtracing/coresight/coresight-tpda.c
>>> index 7baa8a0965d3..f79fea4fbb2c 100644
>>> --- a/drivers/hwtracing/coresight/coresight-tpda.c
>>> +++ b/drivers/hwtracing/coresight/coresight-tpda.c
>>> @@ -430,9 +430,49 @@ static ssize_t syncr_mode_store(struct device *dev,
>>>   }
>>>   static DEVICE_ATTR_RW(syncr_mode);
>>> +static ssize_t port_flush_req_show(struct device *dev,
>>> +                   struct device_attribute *attr,
>>> +                   char *buf)
>>> +{
>>> +    struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
>>> +    unsigned long val;
>>> +
>>> +    if (!drvdata->csdev->refcnt)
>>> +        return -EINVAL;
>>> +
>>> +    guard(spinlock)(&drvdata->spinlock);
>>> +    val = readl_relaxed(drvdata->base + TPDA_FLUSH_CR);
>>> +
>>> +    return sysfs_emit(buf, "0x%lx\n", val);
>>> +}
>>> +
>>> +static ssize_t port_flush_req_store(struct device *dev,
>>> +                    struct device_attribute *attr,
>>> +                    const char *buf,
>>> +                    size_t size)
>>> +{
>>> +    struct tpda_drvdata *drvdata = dev_get_drvdata(dev->parent);
>>> +    u32 val;
>>> +
>>> +    if (kstrtou32(buf, 0, &val))
>>> +        return -EINVAL;
>>> +
>>> +    if (!drvdata->csdev->refcnt || !val)
>>> +        return -EINVAL;
>>> +
>>> +    guard(spinlock)(&drvdata->spinlock);
>>> +    CS_UNLOCK(drvdata->base);
>>> +    writel_relaxed(val, drvdata->base + TPDA_FLUSH_CR);
>>> +    CS_LOCK(drvdata->base);
>>> +
>>> +    return size;
>>> +}
>>> +static DEVICE_ATTR_RW(port_flush_req);
>>> +
>>>   static struct attribute *tpda_attrs[] = {
>>>       &dev_attr_global_flush_req.attr,
>>>       &dev_attr_syncr_mode.attr,
>>> +    &dev_attr_port_flush_req.attr,
>>>       tpda_trig_sysfs_rw(freq_ts_enable, FREQTS),
>>>       tpda_trig_sysfs_rw(trig_freq_enable, FRIE),
>>>       tpda_trig_sysfs_rw(trig_flag_ts_enable, FLRIE),
>>> diff --git a/drivers/hwtracing/coresight/coresight-tpda.h b/drivers/ 
>>> hwtracing/coresight/coresight-tpda.h
>>> index 1d2de50bb9f9..ef1ce2ce36a9 100644
>>> --- a/drivers/hwtracing/coresight/coresight-tpda.h
>>> +++ b/drivers/hwtracing/coresight/coresight-tpda.h
>>> @@ -10,6 +10,7 @@
>>>   #define TPDA_Pn_CR(n)        (0x004 + (n * 4))
>>>   #define TPDA_FPID_CR        (0x084)
>>>   #define TPDA_SYNCR        (0x08C)
>>> +#define TPDA_FLUSH_CR        (0x090)
>>>   /* Cross trigger global (all ports) flush request bit */
>>>   #define TPDA_CR_FLREQ        BIT(0)
>>>
>>
>