Re: [PATCH v3 1/8] hwtracing: Add trace function support for HiSilicon PCIe Tune and Trace device

[Yicong Yang via iommu <iommu@lists.linux-foundation.org>]

On 2022/2/7 19:42, Jonathan Cameron wrote:
> On Mon, 24 Jan 2022 21:11:11 +0800
> Yicong Yang <yangyicong@hisilicon.com> wrote:
> 
>> HiSilicon PCIe tune and trace device(PTT) is a PCIe Root Complex
>> integrated Endpoint(RCiEP) device, providing the capability
>> to dynamically monitor and tune the PCIe traffic, and trace
>> the TLP headers.
>>
>> Add the driver for the device to enable the trace function.
>> This patch adds basic function of trace, including the device's
>> probe and initialization, functions for trace buffer allocation
>> and trace enable/disable, register an interrupt handler to
>> simply response to the DMA events. The user interface of trace
>> will be added in the following patch.
>>
>> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> Hi Yicong,
> 
> I've not been following all the earlier discussion on this driver closely
> so I may well raise something that has already been addressed. If so
> just ignore the comment.

Thanks for the comments. It's ok for me to clarify it :).
Part replies inline and I need to do some test on the others.

> 
> Thanks,
> 
> Jonathan
> 
>> ---
>>  drivers/Makefile                 |   1 +
>>  drivers/hwtracing/Kconfig        |   2 +
>>  drivers/hwtracing/ptt/Kconfig    |  11 +
>>  drivers/hwtracing/ptt/Makefile   |   2 +
>>  drivers/hwtracing/ptt/hisi_ptt.c | 398 +++++++++++++++++++++++++++++++
>>  drivers/hwtracing/ptt/hisi_ptt.h | 159 ++++++++++++
>>  6 files changed, 573 insertions(+)
>>  create mode 100644 drivers/hwtracing/ptt/Kconfig
>>  create mode 100644 drivers/hwtracing/ptt/Makefile
>>  create mode 100644 drivers/hwtracing/ptt/hisi_ptt.c
>>  create mode 100644 drivers/hwtracing/ptt/hisi_ptt.h
>>
[...]
>> +
>> +static int hisi_ptt_alloc_trace_buf(struct hisi_ptt *hisi_ptt)
>> +{
>> +	struct hisi_ptt_trace_ctrl *ctrl = &hisi_ptt->trace_ctrl;
>> +	struct device *dev = &hisi_ptt->pdev->dev;
>> +	struct hisi_ptt_dma_buffer *buffer;
>> +	int i, ret;
>> +
>> +	hisi_ptt->trace_ctrl.buf_index = 0;
>> +
>> +	/* Make sure the trace buffer is empty before allocating */
> 
> This comment is misleading as it suggests it not being empty is
> a bad thing but the code handles it as an acceptable path.
> Perhaps:
> 	/*
> 	 * If the trace buffer has already been allocated, zero the
> 	 * memory.
> 	 */
> 

will make it less misleading. thanks.

>> +	if (!list_empty(&ctrl->trace_buf)) {
>> +		list_for_each_entry(buffer, &ctrl->trace_buf, list)
>> +			memset(buffer->addr, 0, buffer->size);
>> +		return 0;
>> +	}
>> +
>> +	for (i = 0; i < HISI_PTT_TRACE_BUF_CNT; ++i) {
>> +		buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
>> +		if (!buffer) {
>> +			ret = -ENOMEM;
>> +			goto err;
>> +		}
>> +
>> +		buffer->addr = dma_alloc_coherent(dev, ctrl->buffer_size,
>> +						  &buffer->dma, GFP_KERNEL);
>> +		if (!buffer->addr) {
>> +			kfree(buffer);
>> +			ret = -ENOMEM;
>> +			goto err;
>> +		}
>> +
>> +		memset(buffer->addr, 0, buffer->size);
> See:
> https://lore.kernel.org/lkml/20190108130701.14161-4-hch@lst.de/
> dma_alloc_coherent() always zeros the memory for us hence there
> is no longer a dma_kzalloc_coherent()
> 

thanks for the information. Then the memset here is redundant and will drop it.

>> +
>> +		buffer->index = i;
> 
> Carrying an index inside a list which corresponds directly
> to the position in the list is not particularly nice.
> Why can't we compute this index on the fly where the list
> is walked?  Or am I misunderstanding and the order of the buffers
> is changed in a later patch?
> 

The index is fixed once allocated and I stored it to avoid later
computing. But seems it's highly recommended to compute these sort
of things on the fly when necessary. John recommends the same things
on some other places so I think I can get these addressed.

> As a side note, is a list actually appropriate when we always
> have 4 of these buffers?  Feels like an array of buffer
> structures might be cheaper.
> 
>> +		buffer->size = ctrl->buffer_size;
>> +		list_add_tail(&buffer->list, &ctrl->trace_buf);
>> +	}
>> +
>> +	return 0;
>> +err:
>> +	hisi_ptt_free_trace_buf(hisi_ptt);
>> +	return ret;
>> +}
>> +
>> +static void hisi_ptt_trace_end(struct hisi_ptt *hisi_ptt)
>> +{
>> +	writel(0, hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +	hisi_ptt->trace_ctrl.status = HISI_PTT_TRACE_STATUS_OFF;
>> +}
>> +
>> +static int hisi_ptt_trace_start(struct hisi_ptt *hisi_ptt)
>> +{
>> +	struct hisi_ptt_trace_ctrl *ctrl = &hisi_ptt->trace_ctrl;
>> +	struct hisi_ptt_dma_buffer *cur;
>> +	u32 val;
>> +
>> +	/* Check device idle before start trace */
>> +	if (hisi_ptt_wait_trace_hw_idle(hisi_ptt)) {
>> +		pci_err(hisi_ptt->pdev, "Failed to start trace, the device is still busy.\n");
>> +		return -EBUSY;
>> +	}
>> +
>> +	/* Reset the DMA before start tracing */
>> +	val = readl(hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +	val |= HISI_PTT_TRACE_CTRL_RST;
>> +	writel(val, hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +
>> +	/*
>> +	 * We'll be in the perf context where preemption is disabled,
>> +	 * so use busy loop here.
>> +	 */
>> +	mdelay(HISI_PTT_RESET_WAIT_MS);
> 
> Busy look for 1 second?  Ouch.  If we can reduce this in any way
> that would be great or if there is a means to do it before
> we disable preemption.
> 

It's inherited from the previous version that was using msleep() and it's
somehow unacceptable in an atomic context I think. The reset here is
going to reset the write pointer of the hardware DMA so we can check the
whether the pointer before dereset it. I confirmed with our hardware
teams that it can be reduced to 10us. So I'll poll the write pointer register
for about 10us before continue here.

thanks for catching this!

>> +
>> +	val = readl(hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +	val &= ~HISI_PTT_TRACE_CTRL_RST;
>> +	writel(val, hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +
>> +	/* Clear the interrupt status */
>> +	writel(HISI_PTT_TRACE_INT_STAT_MASK, hisi_ptt->iobase + HISI_PTT_TRACE_INT_STAT);
>> +	writel(0, hisi_ptt->iobase + HISI_PTT_TRACE_INT_MASK);
>> +
>> +	/* Configure the trace DMA buffer */
>> +	list_for_each_entry(cur, &ctrl->trace_buf, list) {
> 
> I comment on the use of cur->index above.  Here it would be easy to compute
> the index as we go for example assuming we never end up with holes
> in the list.
> 

ok.

>> +		writel(lower_32_bits(cur->dma),
>> +		       hisi_ptt->iobase + HISI_PTT_TRACE_ADDR_BASE_LO_0 +
>> +		       cur->index * HISI_PTT_TRACE_ADDR_STRIDE);
>> +		writel(upper_32_bits(cur->dma),
>> +		       hisi_ptt->iobase + HISI_PTT_TRACE_ADDR_BASE_HI_0 +
>> +		       cur->index * HISI_PTT_TRACE_ADDR_STRIDE);
>> +	}
>> +	writel(ctrl->buffer_size, hisi_ptt->iobase + HISI_PTT_TRACE_ADDR_SIZE);
>> +
>> +	/* Set the trace control register */
>> +	val = FIELD_PREP(HISI_PTT_TRACE_CTRL_TYPE_SEL, ctrl->type);
>> +	val |= FIELD_PREP(HISI_PTT_TRACE_CTRL_RXTX_SEL, ctrl->direction);
>> +	val |= FIELD_PREP(HISI_PTT_TRACE_CTRL_DATA_FORMAT, ctrl->format);
>> +	val |= FIELD_PREP(HISI_PTT_TRACE_CTRL_TARGET_SEL, hisi_ptt->trace_ctrl.filter);
>> +	if (!hisi_ptt->trace_ctrl.is_port)
>> +		val |= HISI_PTT_TRACE_CTRL_FILTER_MODE;
>> +
>> +	/* Start the Trace */
>> +	val |= HISI_PTT_TRACE_CTRL_EN;
>> +	writel(val, hisi_ptt->iobase + HISI_PTT_TRACE_CTRL);
>> +
>> +	ctrl->status = HISI_PTT_TRACE_STATUS_ON;
>> +
>> +	return 0;
>> +}
>> +
> 
> ...
> 
>> +
>> +static void hisi_ptt_init_ctrls(struct hisi_ptt *hisi_ptt)
>> +{
>> +	struct pci_dev *pdev = hisi_ptt->pdev;
>> +	struct pci_bus *bus;
>> +	u32 reg;
>> +
>> +	INIT_LIST_HEAD(&hisi_ptt->port_filters);
>> +	INIT_LIST_HEAD(&hisi_ptt->req_filters);
>> +
>> +	/*
>> +	 * The device range register provides the information about the
>> +	 * root ports which the RCiEP can control and trace. The RCiEP
>> +	 * and the root ports it support are on the same PCIe core, with
>> +	 * same domain number but maybe different bus number. The device
>> +	 * range register will tell us which root ports we can support,
>> +	 * Bit[31:16] indicates the upper BDF numbers of the root port,
>> +	 * while Bit[15:0] indicates the lower.
>> +	 */
>> +	reg = readl(hisi_ptt->iobase + HISI_PTT_DEVICE_RANGE);
>> +	hisi_ptt->upper = reg >> 16;
>> +	hisi_ptt->lower = reg & 0xffff;
> Trivial:
> Perhaps worthing define HISI_PTT_DEVICE_RANGE_UPPER_MASK etc adn using
> FIELD_GET?
> 

sure.

>> +
>> +	reg = readl(hisi_ptt->iobase + HISI_PTT_LOCATION);
>> +	hisi_ptt->core_id = FIELD_GET(HISI_PTT_CORE_ID, reg);
>> +	hisi_ptt->sicl_id = FIELD_GET(HISI_PTT_SICL_ID, reg);
>> +
>> +	bus = pci_find_bus(pci_domain_nr(pdev->bus), PCI_BUS_NUM(hisi_ptt->upper));
>> +	if (bus)
>> +		pci_walk_bus(bus, hisi_ptt_init_filters, hisi_ptt);
>> +
>> +	/* Initialize trace controls */
>> +	INIT_LIST_HEAD(&hisi_ptt->trace_ctrl.trace_buf);
>> +	hisi_ptt->trace_ctrl.buffer_size = HISI_PTT_TRACE_BUF_SIZE;
>> +	hisi_ptt->trace_ctrl.default_cpu = cpumask_first(cpumask_of_node(dev_to_node(&pdev->dev)));
>> +}
>> +
[...]
>> +
>> +#define HISI_PCIE_CORE_PORT_ID(devfn)	(PCI_FUNC(devfn) << 1)
>> +
>> +enum hisi_ptt_trace_status {
>> +	HISI_PTT_TRACE_STATUS_OFF = 0,
>> +	HISI_PTT_TRACE_STATUS_ON,
>> +};
> 
> Why not just use a boolean given we only have off and on states?
> 

An enum may make the code more readable I think.

Thanks,
Yicong

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