Message-ID: <CAAVeFuLHmYVt870UKPwhdqxi+dJWCskbswwKdVVntDJYkA5YTw@mail.gmail.com>
Date:	Wed, 6 Jul 2016 21:23:30 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Joseph Lo <josephl@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Matthew Longnecker <MLongnecker@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH V2 02/10] mailbox: tegra-hsp: Add HSP(Hardware
 Synchronization Primitives) driver

On Wed, Jul 6, 2016 at 6:06 PM, Joseph Lo <josephl@...dia.com> wrote:
> On 07/06/2016 03:05 PM, Alexandre Courbot wrote:
>>
>> On Tue, Jul 5, 2016 at 6:04 PM, Joseph Lo <josephl@...dia.com> wrote:
>>>
>>> The Tegra HSP mailbox driver implements the signaling doorbell-based
>>> interprocessor communication (IPC) for remote processors currently. The
>>> HSP HW modules support some different features for that, which are
>>> shared mailboxes, shared semaphores, arbitrated semaphores, and
>>> doorbells. And there are multiple HSP HW instances on the chip. So the
>>> driver is extendable to support more features for different IPC
>>> requirement.
>>>
>>> The driver of remote processor can use it as a mailbox client and deal
>>> with the IPC protocol to synchronize the data communications.
>>>
>>> Signed-off-by: Joseph Lo <josephl@...dia.com>
>>> ---
>>> Changes in V2:
>>> - Update the driver to support the binding changes in V2
>>> - it's extendable to support multiple HSP sub-modules on the same HSP HW
>>> block
>>>    now.
>>> ---
>>>   drivers/mailbox/Kconfig     |   9 +
>>>   drivers/mailbox/Makefile    |   2 +
>>>   drivers/mailbox/tegra-hsp.c | 418
>>> ++++++++++++++++++++++++++++++++++++++++++++
>>>   3 files changed, 429 insertions(+)
>>>   create mode 100644 drivers/mailbox/tegra-hsp.c
>>>
>>> diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
>>> index 5305923752d2..fe584cb54720 100644
>>> --- a/drivers/mailbox/Kconfig
>>> +++ b/drivers/mailbox/Kconfig
>>> @@ -114,6 +114,15 @@ config MAILBOX_TEST
>>>            Test client to help with testing new Controller driver
>>>            implementations.
>>>
>>> +config TEGRA_HSP_MBOX
>>> +       bool "Tegra HSP(Hardware Synchronization Primitives) Driver"
>>
>>
>> Space missing before the opening parenthesis (same in the patch title
>> btw).
>
> Okay.
>>
>>
>>> +       depends on ARCH_TEGRA_186_SOC
>>> +       help
>>> +         The Tegra HSP driver is used for the interprocessor
>>> communication
>>> +         between different remote processors and host processors on
>>> Tegra186
>>> +         and later SoCs. Say Y here if you want to have this support.
>>> +         If unsure say N.
>>
>>
>> Since this option is selected automatically by ARCH_TEGRA_186_SOC, you
>> should probably drop the last 2 sentences.
>
> Okay.
>
>>
>>> +
>>>   config XGENE_SLIMPRO_MBOX
>>>          tristate "APM SoC X-Gene SLIMpro Mailbox Controller"
>>>          depends on ARCH_XGENE
>>> diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
>>> index 0be3e742bb7d..26d8f91c7fea 100644
>>> --- a/drivers/mailbox/Makefile
>>> +++ b/drivers/mailbox/Makefile
>>> @@ -25,3 +25,5 @@ obj-$(CONFIG_TI_MESSAGE_MANAGER) += ti-msgmgr.o
>>>   obj-$(CONFIG_XGENE_SLIMPRO_MBOX) += mailbox-xgene-slimpro.o
>>>
>>>   obj-$(CONFIG_HI6220_MBOX)      += hi6220-mailbox.o
>>> +
>>> +obj-${CONFIG_TEGRA_HSP_MBOX}   += tegra-hsp.o
>>> diff --git a/drivers/mailbox/tegra-hsp.c b/drivers/mailbox/tegra-hsp.c
>>> new file mode 100644
>>> index 000000000000..93c3ef58f29f
>>> --- /dev/null
>>> +++ b/drivers/mailbox/tegra-hsp.c
>>> @@ -0,0 +1,418 @@
>>> +/*
>>> + * Copyright (c) 2016, NVIDIA CORPORATION.  All rights reserved.
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> it
>>> + * under the terms and conditions of the GNU General Public License,
>>> + * version 2, as published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope it will be useful, but
>>> WITHOUT
>>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
>>> for
>>> + * more details.
>>> + */
>>> +
>>> +#include <linux/interrupt.h>
>>> +#include <linux/io.h>
>>> +#include <linux/mailbox_controller.h>
>>> +#include <linux/of.h>
>>> +#include <linux/of_device.h>
>>> +#include <linux/platform_device.h>
>>> +#include <dt-bindings/mailbox/tegra186-hsp.h>
>>> +
>>> +#define HSP_INT_DIMENSIONING   0x380
>>> +#define HSP_nSM_OFFSET         0
>>> +#define HSP_nSS_OFFSET         4
>>> +#define HSP_nAS_OFFSET         8
>>> +#define HSP_nDB_OFFSET         12
>>> +#define HSP_nSI_OFFSET         16
>>
>>
>> Would be nice to have comments to understand what SM, SS, AS, etc.
>> stand for (Shared Mailboxes, Shared Semaphores, Arbitrated Semaphores
>> but you need to look at the patch description to understand that). A
>> top-of-file comment explaning the necessary concepts to read this code
>> would do the trick.
>
> Yes, will fix that.
>>
>>
>>> +#define HSP_nINT_MASK          0xf
>>> +
>>> +#define HSP_DB_REG_TRIGGER     0x0
>>> +#define HSP_DB_REG_ENABLE      0x4
>>> +#define HSP_DB_REG_RAW         0x8
>>> +#define HSP_DB_REG_PENDING     0xc
>>> +
>>> +#define HSP_DB_CCPLEX          1
>>> +#define HSP_DB_BPMP            3
>>
>>
>> Maybe turn this into enum and use that type for
>> tegra_hsp_db_chan::db_id? Also have MAX_NUM_HSP_DB here, since it is
>> related to these values?
>
> Okay.
>
>>
>>> +
>>> +#define MAX_NUM_HSP_CHAN 32
>>> +#define MAX_NUM_HSP_DB 7
>>> +
>>> +#define hsp_db_offset(i, d) \
>>> +       (d->base + ((1 + (d->nr_sm >> 1) + d->nr_ss + d->nr_as) << 16) +
>>> \
>>> +       (i) * 0x100)
>>> +
>>> +struct tegra_hsp_db_chan {
>>> +       int master_id;
>>> +       int db_id;
>>> +};
>>> +
>>> +struct tegra_hsp_mbox_chan {
>>> +       int type;
>>> +       union {
>>> +               struct tegra_hsp_db_chan db_chan;
>>> +       };
>>> +};
>>> +
>>> +struct tegra_hsp_mbox {
>>> +       struct mbox_controller *mbox;
>>> +       void __iomem *base;
>>> +       void __iomem *db_base[MAX_NUM_HSP_DB];
>>> +       int db_irq;
>>> +       int nr_sm;
>>> +       int nr_as;
>>> +       int nr_ss;
>>> +       int nr_db;
>>> +       int nr_si;
>>> +       spinlock_t lock;
>>> +};
>>> +
>>> +static inline u32 hsp_readl(void __iomem *base, int reg)
>>> +{
>>> +       return readl(base + reg);
>>> +}
>>> +
>>> +static inline void hsp_writel(void __iomem *base, int reg, u32 val)
>>> +{
>>> +       writel(val, base + reg);
>>> +       readl(base + reg);
>>> +}
>>> +
>>> +static int hsp_db_can_ring(void __iomem *db_base)
>>> +{
>>> +       u32 reg;
>>> +
>>> +       reg = hsp_readl(db_base, HSP_DB_REG_ENABLE);
>>> +
>>> +       return !!(reg & BIT(HSP_DB_MASTER_CCPLEX));
>>> +}
>>> +
>>> +static irqreturn_t hsp_db_irq(int irq, void *p)
>>> +{
>>> +       struct tegra_hsp_mbox *hsp_mbox = p;
>>> +       ulong val;
>>> +       int master_id;
>>> +
>>> +       val = (ulong)hsp_readl(hsp_mbox->db_base[HSP_DB_CCPLEX],
>>> +                              HSP_DB_REG_PENDING);
>>> +       hsp_writel(hsp_mbox->db_base[HSP_DB_CCPLEX], HSP_DB_REG_PENDING,
>>> val);
>>> +
>>> +       spin_lock(&hsp_mbox->lock);
>>> +       for_each_set_bit(master_id, &val, MAX_NUM_HSP_CHAN) {
>>> +               struct mbox_chan *chan;
>>> +               struct tegra_hsp_mbox_chan *mchan;
>>> +               int i;
>>> +
>>> +               for (i = 0; i < MAX_NUM_HSP_CHAN; i++) {
>>
>>
>> I wonder if this could not be optimized. You are doing a double loop
>> on MAX_NUM_HSP_CHAN to look for an identical master_id. Since it seems
>> like the same master_id cannot be used twice (considering that the
>> inner loop only processes the first match), couldn't you just select
>> the free channel in of_hsp_mbox_xlate() by doing
>> &mbox->chans[master_id] (and returning an error if it is already
>> used), then simply getting chan as &hsp_mbox->mbox->chans[master_id]
>> instead of having the inner loop below? That would remove the need for
>> the second loop.
>
>
> That was exactly what I did in the V1, which only supported one HSP
> sub-module per HSP HW block. So we can just use the master_id as the mbox
> channel ID.
>
> Meanwhile, the V2 is purposed to support multiple HSP sub-modules to be
> running on the same HSP HW block. The "ID" between different modules could
> be conflict. So I dropped the mechanism that used the master_id as the mbox
> channel ID.
>
> Instead, the channel is allocated at the time, when the client is bound to
> one of the HSP sub-modules. And we store the "ID" information into the
> private mbox channel data, which can help us to figure out which mbox
> channel should response to the interrupt.
>
> In the doorbell case, because all the DB clients are shared the same DB IRQ
> at the CPU side. So in the ISR, we need to figure out the IRQ source, which
> is the master_id that the IRQ came from. This is the outer loop. The inner
> loop, we figure out which channel should response to by checking the type
> and ID.
>
> And I think it should be pretty quick, because we only check the set bit
> from the pending register. And finding the matching channel.

Yeah, I am not worried about the CPU time (although in interrupt
context, we always should), but rather about whether the code could be
simplified.

Ah, I think I get it. You want to be able to receive interrupts from
the same master, but not necessarily for the doorbell function.
Because of this you cannot use master_id as the index for the channel.
Am I understanding correctly?

>
>>
>> If having two channels use the same master_id is a valid scenario,
>> then all matches on master_id should probably be processed, not just
>> the first one.
>
> Each DB channel should have different master_id.
>
>
>>
>>> +                       chan = &hsp_mbox->mbox->chans[i];
>>> +
>>> +                       if (!chan->con_priv)
>>> +                               continue;
>>> +
>>> +                       mchan = chan->con_priv;
>>> +                       if (mchan->type == HSP_MBOX_TYPE_DB &&
>>> +                           mchan->db_chan.master_id == master_id)
>>> +                               break;
>>> +                       chan = NULL;
>>> +               }
>>> +
>>> +               if (chan)
>>> +                       mbox_chan_received_data(chan, NULL);
>>> +       }
>>> +       spin_unlock(&hsp_mbox->lock);
>>> +
>>> +       return IRQ_HANDLED;
>>> +}
>>> +
>>> +static int hsp_db_send_data(struct mbox_chan *chan, void *data)
>>> +{
>>> +       struct tegra_hsp_mbox_chan *mchan = chan->con_priv;
>>> +       struct tegra_hsp_db_chan *db_chan = &mchan->db_chan;
>>> +       struct tegra_hsp_mbox *hsp_mbox =
>>> dev_get_drvdata(chan->mbox->dev);
>>> +
>>> +       hsp_writel(hsp_mbox->db_base[db_chan->db_id], HSP_DB_REG_TRIGGER,
>>> 1);
>>> +
>>> +       return 0;
>>> +}
>>> +
>>> +static int hsp_db_startup(struct mbox_chan *chan)
>>> +{
>>> +       struct tegra_hsp_mbox_chan *mchan = chan->con_priv;
>>> +       struct tegra_hsp_db_chan *db_chan = &mchan->db_chan;
>>> +       struct tegra_hsp_mbox *hsp_mbox =
>>> dev_get_drvdata(chan->mbox->dev);
>>> +       u32 val;
>>> +       unsigned long flag;
>>> +
>>> +       if (db_chan->master_id >= MAX_NUM_HSP_CHAN) {
>>> +               dev_err(chan->mbox->dev, "invalid HSP chan: master ID:
>>> %d\n",
>>> +                       db_chan->master_id);
>>> +               return -EINVAL;
>>> +       }
>>> +
>>> +       spin_lock_irqsave(&hsp_mbox->lock, flag);
>>> +       val = hsp_readl(hsp_mbox->db_base[HSP_DB_CCPLEX],
>>> HSP_DB_REG_ENABLE);
>>> +       val |= BIT(db_chan->master_id);
>>> +       hsp_writel(hsp_mbox->db_base[HSP_DB_CCPLEX], HSP_DB_REG_ENABLE,
>>> val);
>>> +       spin_unlock_irqrestore(&hsp_mbox->lock, flag);
>>> +
>>> +       if (!hsp_db_can_ring(hsp_mbox->db_base[db_chan->db_id]))
>>> +               return -ENODEV;
>>> +
>>> +       return 0;
>>> +}
>>> +
>>> +static void hsp_db_shutdown(struct mbox_chan *chan)
>>> +{
>>> +       struct tegra_hsp_mbox_chan *mchan = chan->con_priv;
>>> +       struct tegra_hsp_db_chan *db_chan = &mchan->db_chan;
>>> +       struct tegra_hsp_mbox *hsp_mbox =
>>> dev_get_drvdata(chan->mbox->dev);
>>> +       u32 val;
>>> +       unsigned long flag;
>>> +
>>> +       spin_lock_irqsave(&hsp_mbox->lock, flag);
>>> +       val = hsp_readl(hsp_mbox->db_base[HSP_DB_CCPLEX],
>>> HSP_DB_REG_ENABLE);
>>> +       val &= ~BIT(db_chan->master_id);
>>> +       hsp_writel(hsp_mbox->db_base[HSP_DB_CCPLEX], HSP_DB_REG_ENABLE,
>>> val);
>>> +       spin_unlock_irqrestore(&hsp_mbox->lock, flag);
>>> +}
>>> +
>>> +static bool hsp_db_last_tx_done(struct mbox_chan *chan)
>>> +{
>>> +       return true;
>>> +}
>>> +
>>> +static int tegra_hsp_db_init(struct tegra_hsp_mbox *hsp_mbox,
>>> +                            struct mbox_chan *mchan, int master_id)
>>> +{
>>> +       struct platform_device *pdev =
>>> to_platform_device(hsp_mbox->mbox->dev);
>>> +       struct tegra_hsp_mbox_chan *hsp_mbox_chan;
>>> +       int ret;
>>> +
>>> +       if (!hsp_mbox->db_irq) {
>>> +               int i;
>>> +
>>> +               hsp_mbox->db_irq = platform_get_irq_byname(pdev,
>>> "doorbell");
>>
>>
>> Getting the IRQ sounds more like a job for probe() - I don't see the
>> benefit of lazy-doing it?
>
>
> We only need the IRQ when the client is requesting the DB service. For other
> HSP sub-modules, they are using different IRQ. So I didn't do that at probe
> time.

Ok, but probe() is where resources should be acquired... and at the
very least DT properties be looked up. In this case there is no hard
requirement for doing it elsewhere.

Is this interrupt absolutely required? Or can we tolerate to not use
the doorbell service? In the first case, the driver should fail during
probe(), not sometime later. In the second case, you should still get
all the interrupts in probe(), then disable them if they are not
needed, and check in this function whether db_irq is a valid interrupt
number to decide whether or not we can use doorbell.

>
>>
>>> +               ret = devm_request_irq(&pdev->dev, hsp_mbox->db_irq,
>>> +                                      hsp_db_irq, IRQF_NO_SUSPEND,
>>> +                                      dev_name(&pdev->dev), hsp_mbox);
>>> +               if (ret)
>>> +                       return ret;
>>> +
>>> +               for (i = 0; i < MAX_NUM_HSP_DB; i++)
>>> +                       hsp_mbox->db_base[i] = hsp_db_offset(i,
>>> hsp_mbox);
>>
>>
>> Same here, cannot this be moved into probe()?
>
> Same as above, only needed when the client requests it.

But you don't waste any resources by doing it preemptively in probe().
So let's keep related code in the same place.

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