LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Kent Gibson <warthog618@gmail.com>
To: Dipen Patel <dipenp@nvidia.com>
Cc: thierry.reding@gmail.com, jonathanh@nvidia.com,
	linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org,
	linux-gpio@vger.kernel.org, linus.walleij@linaro.org,
	bgolaszewski@baylibre.com, devicetree@vger.kernel.org,
	linux-doc@vger.kernel.org, robh+dt@kernel.org
Subject: Re: [RFC 03/11] hte: Add tegra194 HTE kernel provider
Date: Thu, 1 Jul 2021 22:21:56 +0800	[thread overview]
Message-ID: <20210701142156.GA34285@sol> (raw)
In-Reply-To: <20210625235532.19575-4-dipenp@nvidia.com>

On Fri, Jun 25, 2021 at 04:55:24PM -0700, Dipen Patel wrote:
> Tegra194 device has multiple HTE instances also known as GTE
> (Generic hardware Timestamping Engine) which can timestamp subset of
> SoC lines/signals. This provider driver focuses on IRQ and GPIO lines
> and exposes timestamping ability on those lines to the consumers
> through HTE subsystem.
> 
> Also, with this patch, added:
> - documentation about this provider and its capabilities at
> Documentation/hte.
> - Compilation support in Makefile and Kconfig
> 
> Signed-off-by: Dipen Patel <dipenp@nvidia.com>
> ---
>  Documentation/hte/index.rst        |  21 ++
>  Documentation/hte/tegra194-hte.rst |  65 ++++
>  Documentation/index.rst            |   1 +
>  drivers/hte/Kconfig                |  12 +
>  drivers/hte/Makefile               |   1 +
>  drivers/hte/hte-tegra194.c         | 554 +++++++++++++++++++++++++++++
>  6 files changed, 654 insertions(+)
>  create mode 100644 Documentation/hte/index.rst
>  create mode 100644 Documentation/hte/tegra194-hte.rst
>  create mode 100644 drivers/hte/hte-tegra194.c
> 
> diff --git a/Documentation/hte/index.rst b/Documentation/hte/index.rst
> new file mode 100644
> index 000000000000..f311ebec6b47
> --- /dev/null
> +++ b/Documentation/hte/index.rst
> @@ -0,0 +1,21 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +============================================
> +The Linux Hardware Timestamping Engine (HTE)
> +============================================
> +
> +The HTE Subsystem
> +=================
> +
> +.. toctree::
> +   :maxdepth: 1
> +
> +   hte
> +
> +HTE Tegra Provider
> +==================
> +
> +.. toctree::
> +   :maxdepth: 1
> +
> +   tegra194-hte
> \ No newline at end of file
> diff --git a/Documentation/hte/tegra194-hte.rst b/Documentation/hte/tegra194-hte.rst
> new file mode 100644
> index 000000000000..c23eaafcf080
> --- /dev/null
> +++ b/Documentation/hte/tegra194-hte.rst
> @@ -0,0 +1,65 @@
> +HTE Kernel provider driver
> +==========================
> +
> +Description
> +-----------
> +The Nvidia tegra194 chip has many hardware timestamping engine (HTE) instances
> +known as generic timestamping engine (GTE). This provider driver implements
> +two GTE instances 1) GPIO GTE and 2) IRQ GTE. The both GTEs instances get the
> +timestamp from the system counter TSC which has 31.25MHz clock rate, and the
> +driver converts clock tick rate to nano seconds before storing it as timestamp
> +value.
> +
> +GPIO GTE
> +--------
> +
> +This GTE instance help timestamps GPIO in real time, for that to happen GPIO
> +needs to be configured as input and IRQ needs to ba enabled as well. The only
> +always on (AON) gpio controller instance supports timestamping GPIOs in
> +realtime and it has 39 GPIO lines. There is also a dependency on AON GPIO
> +controller as it requires very specific bits to be set in GPIO config register.
> +It in a way creates cyclic dependency between GTE and GPIO controller. The GTE
> +GPIO functionality is accessed from the GPIOLIB. It can support both the in
> +kernel and userspace consumers. In the later case, requests go through GPIOLIB
> +CDEV framework. The below APIs are added in GPIOLIB framework to access HTE
> +subsystem and GPIO GTE for in kernel consumers.
> +
> +.. c:function:: int gpiod_hw_timestamp_control( struct gpio_desc *desc, bool enable )
> +
> +	To enable HTE on given GPIO line.
> +
> +.. c:function:: u64 gpiod_get_hw_timestamp( struct gpio_desc *desc, bool block )
> +
> +	To retrieve hardwre timestamp in nano seconds.
> +
> +.. c:function:: bool gpiod_is_hw_timestamp_enabled( const struct gpio_desc *desc )
> +
> +	To query if HTE is enabled on the given GPIO.
> +
> +There is hte-tegra194-gpio-test.c, located in ``drivers/hte/`` directory, test
> +driver which demonstrates above APIs for the Jetson AGX platform. For userspace
> +consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HARDWARE flag must be specifed during
> +IOCTL calls, refer ``tools/gpio/gpio-event-mon.c``, which returns the timestamp
> +in nano second.
> +

<snip>

> +
> +static void tegra_hte_read_fifo(struct tegra_hte_soc *gs)
> +{
> +	u32 tsh, tsl, src, pv, cv, acv, slice, bit_index, line_id;
> +	u64 tsc;
> +	int dir;
> +	struct hte_ts_data el;
> +
> +	while ((tegra_hte_readl(gs, HTE_TESTATUS) >>
> +		HTE_TESTATUS_OCCUPANCY_SHIFT) &
> +		HTE_TESTATUS_OCCUPANCY_MASK) {
> +		tsh = tegra_hte_readl(gs, HTE_TETSCH);
> +		tsl = tegra_hte_readl(gs, HTE_TETSCL);
> +		tsc = (((u64)tsh << 32) | tsl);
> +
> +		src = tegra_hte_readl(gs, HTE_TESRC);
> +		slice = (src >> HTE_TESRC_SLICE_SHIFT) &
> +			    HTE_TESRC_SLICE_DEFAULT_MASK;
> +
> +		pv = tegra_hte_readl(gs, HTE_TEPCV);
> +		cv = tegra_hte_readl(gs, HTE_TECCV);
> +		acv = pv ^ cv;
> +		while (acv) {
> +			bit_index = __builtin_ctz(acv);
> +			if ((pv >> bit_index) & BIT(0))
> +				dir = HTE_EVENT_RISING_EDGE;
> +			else
> +				dir = HTE_EVENT_FALLING_EDGE;
> +
> +			line_id = bit_index + (slice << 5);
> +			el.dir = dir;
> +			el.tsc = tsc << HTE_TS_NS_SHIFT;
> +			hte_push_ts_ns_atomic(gs->chip, line_id, &el,
> +					      sizeof(el));
> +			acv &= ~BIT(bit_index);
> +		}
> +		tegra_hte_writel(gs, HTE_TECMD, HTE_TECMD_CMD_POP);
> +	}
> +}

What happens when the hte_push_ts_ns_atomic() fails?
The timestamp will be quietly dropped?
What happens when the interrupt corresponding to that dropped timestamp
asks for it?  The irq handler thread will block until it can get a
timestamp from the subsequent interrupt?

Which brings me back to the concern I have with the approach used in
the hte/gpiolib integration - how do you guarantee that the timestamp
returned by gpiod_get_hw_timestamp() corresponds to the irq interrupt
being handled, particularly in the face of errors such as:
 - overflows of the timestamp FIFO in the chip
 - overflows of software FIFOs as here
 - lost interupts (if the hw generates interrupts faster than the CPU
   can service them)
?

Cheers,
Kent.


  reply	other threads:[~2021-07-01 14:22 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-25 23:55 [RFC 00/11] Intro to Hardware timestamping engine Dipen Patel
2021-06-25 23:55 ` [RFC 01/11] Documentation: Add HTE subsystem guide Dipen Patel
2021-07-04 18:55   ` Jonathan Cameron
2021-07-27 23:44     ` Dipen Patel
2021-08-01 15:24       ` Jonathan Cameron
2021-06-25 23:55 ` [RFC 02/11] drivers: Add HTE subsystem Dipen Patel
2021-06-27 17:40   ` Randy Dunlap
2021-07-04 20:15   ` Jonathan Cameron
2021-07-04 20:45     ` Jonathan Cameron
2021-07-28  5:12       ` Dipen Patel
2021-08-01 16:48         ` Jonathan Cameron
2021-07-28  4:38     ` Dipen Patel
2021-08-01 16:13       ` Jonathan Cameron
2021-09-14  5:43         ` Dipen Patel
2021-09-26 15:42           ` Jonathan Cameron
2021-07-05  7:30   ` Greg KH
2021-07-28  0:34     ` Dipen Patel
2021-06-25 23:55 ` [RFC 03/11] hte: Add tegra194 HTE kernel provider Dipen Patel
2021-07-01 14:21   ` Kent Gibson [this message]
2021-07-28 23:59     ` Dipen Patel
2021-07-30  7:01       ` Dipen Patel
2021-07-31 15:43       ` Kent Gibson
2021-08-03 22:40         ` Dipen Patel
2021-08-03 23:02           ` Kent Gibson
2021-08-07  2:41         ` Dipen Patel
2021-08-07  3:07           ` Kent Gibson
2021-08-07  4:52             ` Dipen Patel
2021-08-07  4:51               ` Kent Gibson
2021-08-07  5:35                 ` Dipen Patel
2021-08-07  5:42                   ` Kent Gibson
2021-08-07  5:47                   ` Dipen Patel
2021-07-04 20:27   ` Jonathan Cameron
2021-07-29  2:42     ` Dipen Patel
2021-07-08 23:33   ` Michał Mirosław
2021-07-29  2:43     ` Dipen Patel
2021-06-25 23:55 ` [RFC 04/11] dt-bindings: Add HTE bindings Dipen Patel
2021-06-27 10:56   ` Linus Walleij
2021-07-30  1:32     ` Dipen Patel
2021-07-01 14:02   ` Rob Herring
2021-07-30  1:56     ` Dipen Patel
2021-07-01 15:54   ` Rob Herring
2021-07-30  1:58     ` Dipen Patel
2021-06-25 23:55 ` [RFC 05/11] hte: Add Tegra194 IRQ HTE test driver Dipen Patel
2021-06-27 17:42   ` Randy Dunlap
2021-06-25 23:55 ` [RFC 06/11] gpiolib: Add HTE support Dipen Patel
2021-06-27 11:41   ` Linus Walleij
2021-07-01 14:24   ` Kent Gibson
2021-07-30  2:25     ` Dipen Patel
2021-07-31  5:13       ` Kent Gibson
2021-06-25 23:55 ` [RFC 07/11] gpio: tegra186: Add HTE in gpio-tegra186 driver Dipen Patel
2021-06-25 23:55 ` [RFC 08/11] gpiolib: cdev: Add hardware timestamp clock type Dipen Patel
2021-06-27 11:38   ` Linus Walleij
2021-06-27 11:49   ` Linus Walleij
2021-07-30  3:16     ` Dipen Patel
2021-07-01 14:24   ` Kent Gibson
2021-07-30  3:07     ` Dipen Patel
2021-07-31  6:05       ` Kent Gibson
2021-08-03 22:41         ` Dipen Patel
2021-08-03 22:38           ` Kent Gibson
2021-07-09  8:30   ` Jon Hunter
2021-07-30  2:33     ` Dipen Patel
2021-08-03 16:42       ` Jon Hunter
2021-08-03 22:51         ` Dipen Patel
2021-08-03 23:09           ` Kent Gibson
2021-06-25 23:55 ` [RFC 09/11] tools: gpio: Add new hardware " Dipen Patel
2021-06-27 11:36   ` Linus Walleij
2021-07-30  3:17     ` Dipen Patel
2021-07-31  6:16       ` Kent Gibson
2021-08-11  9:11         ` Linus Walleij
2021-06-25 23:55 ` [RFC 10/11] hte: Add tegra GPIO HTE test driver Dipen Patel
2021-06-27 17:43   ` Randy Dunlap
2021-06-25 23:55 ` [RFC 11/11] MAINTAINERS: Added HTE Subsystem Dipen Patel
2021-06-27 13:07 ` [RFC 00/11] Intro to Hardware timestamping engine Andy Shevchenko
2021-06-27 14:40   ` Linus Walleij
2021-06-28 12:02     ` Andy Shevchenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210701142156.GA34285@sol \
    --to=warthog618@gmail.com \
    --cc=bgolaszewski@baylibre.com \
    --cc=devicetree@vger.kernel.org \
    --cc=dipenp@nvidia.com \
    --cc=jonathanh@nvidia.com \
    --cc=linus.walleij@linaro.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-gpio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-tegra@vger.kernel.org \
    --cc=robh+dt@kernel.org \
    --cc=thierry.reding@gmail.com \
    --subject='Re: [RFC 03/11] hte: Add tegra194 HTE kernel provider' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).