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

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Message-ID: <b3b1e130-4592-4863-825f-e00cb9d996b8@oss.qualcomm.com>
Date: Tue, 23 Dec 2025 10:16:36 +0800
From: Jie Gan <jie.gan@....qualcomm.com>
To: Suzuki K Poulose <suzuki.poulose@....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 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.

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)
>>
>