From patchwork Tue Feb 28 10:03:01 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: =?utf-8?b?S09OUkFEIEZyw6lkw6lyaWM=?= X-Patchwork-Id: 9595049 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 34C2A60429 for ; Tue, 28 Feb 2017 10:04:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 10CD728174 for ; Tue, 28 Feb 2017 10:04:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 03DF128518; Tue, 28 Feb 2017 10:04:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 0AD3728174 for ; Tue, 28 Feb 2017 10:04:15 +0000 (UTC) Received: from localhost ([::1]:59849 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ciedi-0006qD-5F for patchwork-qemu-devel@patchwork.kernel.org; Tue, 28 Feb 2017 05:04:14 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58931) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cied6-0006oW-CA for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:03:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cied4-00048t-WF for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:03:36 -0500 Received: from greensocs.com ([193.104.36.180]:38421) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cied4-00048g-Iq for qemu-devel@nongnu.org; Tue, 28 Feb 2017 05:03:34 -0500 Received: from localhost (localhost [127.0.0.1]) by greensocs.com (Postfix) with ESMTP id E1688425197; Tue, 28 Feb 2017 11:03:33 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=greensocs.com; s=mail; t=1488276213; bh=wvVpIGEINmH4uvSZQEAA/AgLWj0FETGispOsHvJiqd8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oDEYS596o+BibGaPrU52XkdTiGzpwdTN4tFovMEYjvSwYbtbmdsaPd1VAt6uDmCzL tmZ8bNWDAeTU89gCkNLiq7EwL5wIUFDuq8IwIILIw4qnPykYOiRAqAJZFrK45kIpRj FndR655aFhavtLHuQdenqWVkyzmo8US/Qb4uSQ4Q= X-Virus-Scanned: amavisd-new at greensocs.com Authentication-Results: gs-01.greensocs.com (amavisd-new); dkim=pass (1024-bit key) header.d=greensocs.com Received: from greensocs.com ([127.0.0.1]) by localhost (gs-01.greensocs.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id F0zjqDOA1P7x; Tue, 28 Feb 2017 11:03:33 +0100 (CET) Received: from corsair.home (bd231-7-88-127-3-24.fbx.proxad.net [88.127.3.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: fred.konrad@greensocs.com) by greensocs.com (Postfix) with ESMTPSA id 5BFD53FE898; Tue, 28 Feb 2017 11:03:32 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=greensocs.com; s=mail; t=1488276212; bh=wvVpIGEINmH4uvSZQEAA/AgLWj0FETGispOsHvJiqd8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=5DeI2Uh+x2s0bcyur+HFlx+qKl4qFGY6I6cWpVrlXBkhYG5PE8A/o04r4FFK+U3AP TPBhz0uPShkTyQw8ZCH17VNdVxoMXTGAp4rUb+k0kFaj5fPT3JOQgJTZM/WF1XDA4t YxCOmtccKas0houjeYyO9Uu1kpdZJreWXHz551tI= From: fred.konrad@greensocs.com To: qemu-devel@nongnu.org Date: Tue, 28 Feb 2017 11:03:01 +0100 Message-Id: <1488276185-31168-7-git-send-email-fred.konrad@greensocs.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1488276185-31168-1-git-send-email-fred.konrad@greensocs.com> References: <1488276185-31168-1-git-send-email-fred.konrad@greensocs.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 193.104.36.180 Subject: [Qemu-devel] [PATCH v3 06/10] docs: add qemu-clock documentation X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: edgar.iglesias@xilinx.com, peter.maydell@linaro.org, mark.burton@greensocs.com, alistair.francis@xilinx.com, clg@kaod.org, fred.konrad@greensocs.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: KONRAD Frederic This adds the qemu-clock documentation. Signed-off-by: KONRAD Frederic V1 -> V2: * Fixed in accordance with the changes in the previous patches. --- docs/clock.txt | 278 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 278 insertions(+) create mode 100644 docs/clock.txt diff --git a/docs/clock.txt b/docs/clock.txt new file mode 100644 index 0000000..010ae50 --- /dev/null +++ b/docs/clock.txt @@ -0,0 +1,278 @@ + +What is a QEMU_CLOCK +==================== + +A QEMU_CLOCK is a QOM Object developed for the purpose of modeling a clock tree +with QEMU. + +It only simulates the clock by keeping a copy of the current frequency and +doesn't model the signal itself such as pin toggle or duty cycle. + +It allows to model the impact of badly configured PLL, clock source selection +or disabled clock on the models. + +Binding the clock together to create a tree +=========================================== + +In order to create a clock tree with QEMU_CLOCK two or more clock must be bound +together. Let's say there are two clocks clk_a and clk_b: +Using qemu_clk_bind(clk_a, clk_b) will bind clk_a and clk_b. + +Binding two qemu-clk together creates a unidirectional link which means that +changing the rate of clk_a will propagate to clk_b and not the opposite. +The binding process automatically refreshes clk_b rate. + +Clock can be bound and unbound during execution for modeling eg: a clock +selector. + +A clock can drive more than one other clock. eg with this code: +qemu_clk_bind(clk_a, clk_b); +qemu_clk_bind(clk_a, clk_c); + +A clock rate change one clk_a will propagate to clk_b and clk_c. + +Implementing a callback on a rate change +======================================== + +The function prototype is the following: +typedef uint64_t QEMUClkRateUpdateCallback(void *opaque, uint64_t rate); + +It's main goal is to modify the rate before it's passed to the next clocks in +the tree. + +eg: for a 4x PLL the function will be: +uint64_t qemu_clk_rate_change_cb(void *opaque, uint64_t rate) +{ + return 4 * rate; +} + +To set the callback for the clock: +void qemu_clk_set_callback(qemu_clk clk, QEMUClkRateUpdateCallback *cb, + void *opaque); +can be called. + +The rate update process +======================= + +The rate update happen in this way: +When a model wants to update a clock frequency (eg: based on a register change +or something similar) it will call qemu_clk_update_rate(..) on the clock: + * The callback associated to the clock is called with the new rate. + * qemu_clk_update_rate(..) is then called on all bound clocks with the value + returned by the callback. + +NOTE: When no callback is attached, the clock qemu_clk_update_rate(..) is called +on the next clock in the tree with the rate unmodified. + +Adding a QEMU_CLOCK to a DeviceState +==================================== + +Adding a qemu-clk to a DeviceState is required to be able to get the clock +outside the model through qemu_clk_device_get_clock(..). + +It is also required to be able to print the clock and its rate with info qtree. +For example: + + type System + dev: xlnx.zynqmp_crf, id "" + gpio-out "sysbus-irq" 1 + gpio-out "RST_A9" 4 + qemu-clk "dbg_trace" 0 + qemu-clk "vpll_to_lpd" 625000000 + qemu-clk "dp_stc_ref" 0 + qemu-clk "dpll_to_lpd" 12500000 + qemu-clk "acpu_clk" 0 + qemu-clk "pcie_ref" 0 + qemu-clk "topsw_main" 0 + qemu-clk "topsw_lsbus" 0 + qemu-clk "dp_audio_ref" 0 + qemu-clk "sata_ref" 0 + qemu-clk "dp_video_ref" 71428568 + qemu-clk "vpll_clk" 2500000000 + qemu-clk "apll_to_lpd" 12500000 + qemu-clk "dpll_clk" 50000000 + qemu-clk "gpu_ref" 0 + qemu-clk "aux_refclk" 0 + qemu-clk "video_clk" 27000000 + qemu-clk "gdma_ref" 0 + qemu-clk "gt_crx_ref_clk" 0 + qemu-clk "dbg_fdp" 0 + qemu-clk "apll_clk" 50000000 + qemu-clk "pss_alt_ref_clk" 0 + qemu-clk "ddr" 0 + qemu-clk "pss_ref_clk" 50000000 + qemu-clk "dpdma_ref" 0 + qemu-clk "dbg_tstmp" 0 + mmio 00000000fd1a0000/000000000000010c + +This way a DeviceState can have multiple clock input or output. + +Examples +======== + +Those are the different way of using the QEMUClock object. + +Modelling a fixed clock generator +================================= + +Here is a brief example of a device acting as a clock source: + +typedef struct { + DeviceState parent_obj; + + uint32_t rate; + QEMUClock out; +} FixedClock; + +During the initialization the device must initialize its clock object: + +static void fixed_clock_instance_init(Object *obj) +{ + FixedClock *s = FIXED_CLOCK(obj); + + object_initialize(&s->out, sizeof(s->out), TYPE_CLOCK); + qemu_clk_device_add_clock(DEVICE(obj), &s->out, "clk_out"); +} + +As the device acts as a clock source it must refresh the clock tree during the +realize phase: + +static void fixed_clock_realizefn(DeviceState *dev, Error **errp) +{ + FixedClock *s = FIXED_CLOCK(dev); + + qemu_clk_update_rate(&s->out, s->rate); +} + +This means that the clock tree must be finished before realize is called on the +fixed clock. + +Modelling a clock user device +============================= + +Here is a brief example of a clock user: + +typedef struct { + DeviceState parent_obj; + + QEMUClock in; +} ClockUser; + +As before the clock must be initialized through the device initialize function: + +static void clock_user_instance_init(Object *obj) +{ + ClockUser *s = CLOCK_USER(obj); + + object_initialize(&s->in, sizeof(s->in), TYPE_CLOCK); + qemu_clk_device_add_clock(DEVICE(obj), &s->in, "clk_in"); + /* + * Call on_rate_change_cb when something change on clk_in. + */ + qemu_clk_set_callback(s->in, on_rate_change_cb, obj); +} + +The callback is in this case used as a notifier when the clock tree which +sources the device change: + +static uint64_t on_rate_change_cb(void *opaque, uint64_t input_rate) +{ + printf("the new rate is %ld\n", input_rate); + + /* The return is ignored if nothing is bound to clk_in. */ + return input_rate; +} + +Modelling a clock multiplier +============================ + +Here is a brief example of a device acting as a clock modifier: + +typedef struct { + DeviceState parent_obj; + + uint32_t rate; + QEMUClock out; + QEMUClock in; +} ClockMultiplier; + +As before the clocks must be initialized through the device initialize function +but they must be bound together so a change on the input will propagate on the +output: + +static void clock_multiplier_instance_init(Object *obj) +{ + ClockMultiplier *s = CLOCK_MULTIPLIER(obj); + + object_initialize(&s->out, sizeof(s->out), TYPE_CLOCK); + object_initialize(&s->in, sizeof(s->in), TYPE_CLOCK); + + qemu_clk_device_add_clock(DEVICE(obj), &s->in, "clk_in"); + qemu_clk_device_add_clock(DEVICE(obj), &s->out, "clk_out"); + /* + * Propagate the change from in to out, this can be done dynamically during + * the simulation but we need to do the initial binding here to get the + * initial refresh happening when the realize function is called on the + * fixed clock. + */ + qemu_clk_bind(s->in, s->out); + /* + * But before propagating the rate modify it with multiplier_cb. + */ + qemu_clk_set_callback(s->out, multiplier_cb, obj); +} + +In this example when clk_in changes it will trigger a change on clk_out and this +callback can modify the rate of clk_out (the return value of this callback) +accordingly to clk_in rate (input_rate). + +static uint64_t multiplier_cb(void *opaque, uint64_t input_rate) +{ + return input_rate * 4; +} + +This device doesn't refresh the clock tree as it will be done by the clock tree +source. + +Modelling a clock selector +========================== + +Here is a brief example of a device acting as a device which alter the clock +topology such as a clock selector: + +typedef struct { + DeviceState parent_obj; + + QEMUClock out; + QEMUClock in_a; + QEMUClock in_b; +} ClockSelector; + +The clocks must be initialized through the device initialize function but they +must be bound together like they will be when the device is reset so a change on +the input during the realize of the fixed clock will propagate to the output: + +static void clock_selector_instance_init(Object *obj) +{ + ClockSelector *s = CLOCK_SELECTOR(obj); + + object_initialize(&s->out, sizeof(s->out), TYPE_CLOCK); + object_initialize(&s->in_a, sizeof(s->in_a), TYPE_CLOCK); + object_initialize(&s->in_b, sizeof(s->in_b), TYPE_CLOCK); + + qemu_clk_device_add_clock(DEVICE(obj), &s->in_a, "clk_in_a"); + qemu_clk_device_add_clock(DEVICE(obj), &s->in_b, "clk_in_b"); + qemu_clk_device_add_clock(DEVICE(obj), &s->out, "clk_out"); + + /* Assuming at the reset that the input_a is connected to output. */ + qemu_clk_bind(s->in_a, s->out); +} + +/* This is called for example by a register change or something like that */ +void update_topology(ClockSelector *s) +{ + /* Unbind the old clock */ + qemu_clk_unbind(s->in_a, s->out); + /* Bind the new one, the rate is automatically refreshed. */ + qemu_clk_bind(s->in_b, s->out); +}