Message-ID: <CAJe_ZhfaLqgKb3oK-m5Rpae5+zeAEk9-DLFOovq4qjBgg64b-w@mail.gmail.com>
Date:	Wed, 23 Jul 2014 20:30:53 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Devicetree List <devicetree@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"ks.giri@...sung.com" <ks.giri@...sung.com>,
	Arnd Bergmann <arnd@...db.de>, ijc@...lion.org.uk,
	Mark Rutland <mark.rutland@....com>, robh@...nel.org,
	Pawel Moll <pawel.moll@....com>,
	Courtney Cavin <courtney.cavin@...ymobile.com>,
	Matt Porter <mporter@...aro.org>,
	Craig McGeachie <slapdau@...oo.com.au>,
	LeyFoon Tan <lftan.linux@...il.com>,
	Loic Pallardy <loic.pallardy@...com>,
	"Anna, Suman" <s-anna@...com>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Bjorn Andersson <bjorn@...o.se>,
	Patch Tracking <patches@...aro.org>,
	Tetsuya Takinishi <t.takinishi@...fujitsu.com>,
	Mark Brown <broonie@...aro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Mollie Wu <mollie.wu@...aro.org>,
	Andy Green <andy.green@...aro.org>
Subject: Re: [PATCHv9 2/4] mailbox: Introduce framework for mailbox

On 23 July 2014 14:24, Lee Jones <lee.jones@...aro.org> wrote:
> On Wed, 23 Jul 2014, Jassi Brar wrote:
>> Introduce common framework for client/protocol drivers and
>> controller drivers of Inter-Processor-Communication (IPC).
>>
>> Client driver developers should have a look at
>>  include/linux/mailbox_client.h to understand the part of
>> the API exposed to client drivers.
>> Similarly controller driver developers should have a look
>> at include/linux/mailbox_controller.h
>>
>> Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
>> ---
>>  MAINTAINERS                        |   8 +
>>  drivers/mailbox/Makefile           |   4 +
>>  drivers/mailbox/mailbox.c          | 467 +++++++++++++++++++++++++++++++++++++
>>  include/linux/mailbox_client.h     |  45 ++++
>>  include/linux/mailbox_controller.h | 131 +++++++++++
>>  5 files changed, 655 insertions(+)
>>  create mode 100644 drivers/mailbox/mailbox.c
>>  create mode 100644 include/linux/mailbox_client.h
>>  create mode 100644 include/linux/mailbox_controller.h
>
> After a _quick_ look through:
>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 61a8f48..9f225d2 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -5672,6 +5672,14 @@ S:     Maintained
>>  F:   drivers/net/macvlan.c
>>  F:   include/linux/if_macvlan.h
>>
>> +MAILBOX API
>> +M:   Jassi Brar <jassisinghbrar@...il.com>
>
> Gmail?
>
Yup, as much as I am grateful to Linaro for giving me the opportunity
to work on this... the unfortunate fact remains that every, but the
personal, email-id eventually starts bouncing mails :)
Please note the copyright is owned by Linaro as it should be.

>> +L:   linux-kernel@...r.kernel.org
>> +S:   Maintained
>> +F:   drivers/mailbox/
>> +F:   include/linux/mailbox_client.h
>> +F:   include/linux/mailbox_controller.h
>> +
>
> [...]
>
>> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
>> new file mode 100644
>> index 0000000..99c0d23
>> --- /dev/null
>> +++ b/drivers/mailbox/mailbox.c
>> @@ -0,0 +1,467 @@
>> +/*
>> + * Mailbox: Common code for Mailbox controllers and users
>> + *
>> + * Copyright (C) 2013-2014 Linaro Ltd.
>> + * Author: Jassi Brar <jassisinghbrar@...il.com>
>
> (C) Linaro, but you've supplied your Gmail?
>
I don't understand how that's a problem. Is it?
I always try to post from my Linaro id still.

>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <linux/interrupt.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/mutex.h>
>> +#include <linux/delay.h>
>> +#include <linux/slab.h>
>> +#include <linux/err.h>
>> +#include <linux/module.h>
>> +#include <linux/device.h>
>> +#include <linux/mailbox_client.h>
>> +#include <linux/mailbox_controller.h>
>> +
>> +#define TXDONE_BY_IRQ        (1 << 0) /* controller has remote RTR irq */
>> +#define TXDONE_BY_POLL       (1 << 1) /* controller can read status of last TX */
>> +#define TXDONE_BY_ACK        (1 << 2) /* S/W ACK recevied by Client ticks the TX */
>
> BIT(0), BIT(1), BIT(2).
>
Yeah that would look cooler.

>> +static LIST_HEAD(mbox_cons);
>> +static DEFINE_MUTEX(con_mutex);
>> +
>> +static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
>> +{
>> +     int idx;
>> +     unsigned long flags;
>> +
>> +     spin_lock_irqsave(&chan->lock, flags);
>> +
>> +     /* See if there is any space left */
>> +     if (chan->msg_count == MBOX_TX_QUEUE_LEN) {
>> +             spin_unlock_irqrestore(&chan->lock, flags);
>> +             return -ENOMEM;
>
> Doesn't -ENOMEM signify out-of-system-memory, rather than a buffer has
> been filled?  I'm thinking ENOBUFS would be more appropriate.
>
OK :)

>> +     }
>> +
>> +     idx = chan->msg_free;
>> +     chan->msg_data[idx] = mssg;
>> +     chan->msg_count++;
>> +
>> +     if (idx == MBOX_TX_QUEUE_LEN - 1)
>> +             chan->msg_free = 0;
>> +     else
>> +             chan->msg_free++;
>> +
>> +     spin_unlock_irqrestore(&chan->lock, flags);
>> +
>> +     return idx;
>> +}
>> +
>> +static void msg_submit(struct mbox_chan *chan)
>> +{
>> +     unsigned count, idx;
>> +     unsigned long flags;
>> +     void *data;
>> +     int err;
>> +
>> +     spin_lock_irqsave(&chan->lock, flags);
>> +
>> +     if (!chan->msg_count || chan->active_req) {
>> +             spin_unlock_irqrestore(&chan->lock, flags);
>> +             return;
>> +     }
>
> You could reduce by a line here if you use a goto, to jump down to the
> other spin_unlock*().
>
Thanks

>> +     count = chan->msg_count;
>> +     idx = chan->msg_free;
>> +     if (idx >= count)
>> +             idx -= count;
>> +     else
>> +             idx += MBOX_TX_QUEUE_LEN - count;
>> +
>> +     data = chan->msg_data[idx];
>> +
>> +     /* Try to submit a message to the MBOX controller */
>> +     err = chan->mbox->ops->send_data(chan, data);
>> +     if (!err) {
>> +             chan->active_req = data;
>> +             chan->msg_count--;
>> +     }
>
> How do we let the caller know if an error occured?
>
Messages are only expected to be queued, not sent from the submit
call. So we eventually let the user know something bad happened via
timeout.

>> +     spin_unlock_irqrestore(&chan->lock, flags);
>> +}
>
> [...]
>
>> +static void poll_txdone(unsigned long data)
>> +{
>> +     struct mbox_controller *mbox = (struct mbox_controller *)data;
>> +     bool txdone, resched = false;
>> +     int i;
>> +
>> +     for (i = 0; i < mbox->num_chans; i++) {
>> +             struct mbox_chan *chan = &mbox->chans[i];
>> +
>> +             if (chan->active_req && chan->cl) {
>> +                     resched = true;
>> +                     txdone = chan->mbox->ops->last_tx_done(chan);
>
> You should probably add a comment somewhere that this operation is
> compulsory.  Same for all of the other mandatory call-backs.
>
I thought I rather marked some calls as optional.

>> +                     if (txdone)
>> +                             tx_tick(chan, 0);
>> +             }
>> +     }
>> +
>> +     if (resched)
>> +             mod_timer(&mbox->poll, jiffies +
>> +                             msecs_to_jiffies(mbox->period));
>> +}
>
> [...]
>
>> +/**
>> + * mbox_send_message -       For client to submit a message to be
>> + *                           sent to the remote.
>> + * @chan: Mailbox channel assigned to this client.
>> + * @mssg: Client specific message typecasted.
>> + *
>> + * For client to submit data to the controller destined for a remote
>> + * processor. If the client had set 'tx_block', the call will return
>> + * either when the remote receives the data or when 'tx_tout' millisecs
>> + * run out.
>> + *  In non-blocking mode, the requests are buffered by the API and a
>> + * non-negative token is returned for each queued request. If the request
>> + * is not queued, a negative token is returned. Upon failure or successful
>> + * TX, the API calls 'tx_done' from atomic context, from which the client
>> + * could submit yet another request.
>> + * The pointer to message should be preserved until it is sent
>> + * over the chan, i.e, tx_done() is made.
>> + * This function could be called from atomic context as it simply
>> + * queues the data and returns a token against the request.
>> + *
>> + * Return: Non-negative integer for successful submission (non-blocking mode)
>> + *   or transmission over chan (blocking mode).
>> + *   Negative value denotes failure.
>> + */
>> +int mbox_send_message(struct mbox_chan *chan, void *mssg)
>> +{
>> +     int t;
>> +
>> +     if (!chan || !chan->cl)
>> +             return -EINVAL;
>> +
>> +     t = add_to_rbuf(chan, mssg);
>> +     if (t < 0) {
>> +             pr_err("Try increasing MBOX_TX_QUEUE_LEN\n");
>
> Really?
>
Yup. There's a rich bikeshedding history of more than a year in the
archives, over this rather simple aspect.


>> +             return t;
>> +     }
>> +
>> +     msg_submit(chan);
>> +
>> +     reinit_completion(&chan->tx_complete);
>> +
>> +     if (chan->txdone_method == TXDONE_BY_POLL)
>> +             poll_txdone((unsigned long)chan->mbox);
>> +
>> +     if (chan->cl->tx_block && chan->active_req) {
>> +             unsigned long wait;
>> +             int ret;
>> +
>> +             if (!chan->cl->tx_tout) /* wait for ever */
>
> s/for ever/forever
>
thanks

>> +                     wait = msecs_to_jiffies(3600000);
>
> What will this do?  Will it block the system forever?
>
Only if the user wanted the message xfer to be blocking but didn't
care to specify the timeout.

>> +             else
>> +                     wait = msecs_to_jiffies(chan->cl->tx_tout);
>> +
>> +             ret = wait_for_completion_timeout(&chan->tx_complete, wait);
>> +             if (ret == 0) {
>> +                     t = -EIO;
>> +                     tx_tick(chan, -EIO);
>> +             }
>> +     }
>> +
>> +     return t;
>> +}
>> +EXPORT_SYMBOL_GPL(mbox_send_message);
>> +
>> +/**
>> + * mbox_request_channel - Request a mailbox channel.
>> + * @cl: Identity of the client requesting the channel.
>> + * @index: Index of mailbox specifier in 'mboxes' property.
>> + *
>> + * The Client specifies its requirements and capabilities while asking for
>> + * a mailbox channel. It can't be called from atomic context.
>> + * The channel is exclusively allocated and can't be used by another
>> + * client before the owner calls mbox_free_channel.
>> + * After assignment, any packet received on this channel will be
>> + * handed over to the client via the 'rx_callback'.
>> + * The framework holds reference to the client, so the mbox_client
>> + * structure shouldn't be modified until the mbox_free_channel returns.
>> + *
>> + * Return: Pointer to the channel assigned to the client if successful.
>> + *           ERR_PTR for request failure.
>> + */
>> +struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
>> +{
>> +     struct device *dev = cl->dev;
>> +     struct mbox_controller *mbox;
>> +     struct of_phandle_args spec;
>> +     struct mbox_chan *chan;
>> +     unsigned long flags;
>> +     int ret;
>> +
>> +     if (!dev || !dev->of_node) {
>> +             pr_debug("%s: No owner device node\n", __func__);
>
> Are you sure you want all of this debug prints in the final version?
>
pr_debug is as good as absent unless DEBUG is defined

>> +             return ERR_PTR(-ENODEV);
>> +     }
>> +
>> +     mutex_lock(&con_mutex);
>> +
>> +     if (of_parse_phandle_with_args(dev->of_node, "mboxes",
>> +                                    "#mbox-cells", index, &spec)) {
>> +             pr_debug("%s: can't parse \"mboxes\" property\n", __func__);
>
> How you have a 'struct device' to play with, can't you use dev_dbg()
> and friends?
>
At some places we don't/can't, so same here.

>> +             mutex_unlock(&con_mutex);
>> +             return ERR_PTR(-ENODEV);
>> +     }
>> +
>> +     chan = NULL;
>
> Do this during declaration.
>
>> +     list_for_each_entry(mbox, &mbox_cons, node)
>> +             if (mbox->dev->of_node == spec.np) {
>> +                     chan = mbox->of_xlate(mbox, &spec);
>> +                     break;
>> +             }
>> +
>> +     of_node_put(spec.np);
>> +
>> +     if (!chan || chan->cl || !try_module_get(mbox->dev->driver->owner)) {
>> +             pr_debug("%s: mailbox not free\n", __func__);
>> +             mutex_unlock(&con_mutex);
>> +             return ERR_PTR(-EBUSY);
>> +     }
>> +
>> +     spin_lock_irqsave(&chan->lock, flags);
>> +     chan->msg_free = 0;
>> +     chan->msg_count = 0;
>> +     chan->active_req = NULL;
>> +     chan->cl = cl;
>> +     init_completion(&chan->tx_complete);
>> +
>> +     if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
>> +             chan->txdone_method |= TXDONE_BY_ACK;
>> +
>> +     spin_unlock_irqrestore(&chan->lock, flags);
>> +
>> +     ret = chan->mbox->ops->startup(chan);
>> +     if (ret) {
>> +             pr_err("Unable to startup the chan (%d)\n", ret);
>> +             mbox_free_channel(chan);
>> +             chan = ERR_PTR(ret);
>> +     }
>> +
>> +     mutex_unlock(&con_mutex);
>> +     return chan;
>> +}
>> +EXPORT_SYMBOL_GPL(mbox_request_channel);
>> +
>> +/**
>> + * mbox_free_channel - The client relinquishes control of a mailbox
>> + *                   channel by this call.
>> + * @chan: The mailbox channel to be freed.
>> + */
>> +void mbox_free_channel(struct mbox_chan *chan)
>> +{
>> +     unsigned long flags;
>> +
>> +     if (!chan || !chan->cl)
>> +             return;
>> +
>> +     chan->mbox->ops->shutdown(chan);
>> +
>> +     /* The queued TX requests are simply aborted, no callbacks are made */
>> +     spin_lock_irqsave(&chan->lock, flags);
>> +     chan->cl = NULL;
>> +     chan->active_req = NULL;
>> +     if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
>> +             chan->txdone_method = TXDONE_BY_POLL;
>
> Unless you're leaving it there for clarity, you can drop the
> "TXDONE_BY_POLL |" from if().
>
We need to check for both.

>> +     module_put(chan->mbox->dev->driver->owner);
>> +     spin_unlock_irqrestore(&chan->lock, flags);
>> +}
>> +EXPORT_SYMBOL_GPL(mbox_free_channel);
>> +
>> +static struct mbox_chan *
>> +of_mbox_index_xlate(struct mbox_controller *mbox,
>> +                 const struct of_phandle_args *sp)
>> +{
>> +     int ind = sp->args[0];
>> +
>> +     if (ind >= mbox->num_chans)
>> +             return NULL;
>> +
>> +     return &mbox->chans[ind];
>> +}
>> +
>> +/**
>> + * mbox_controller_register - Register the mailbox controller
>> + * @mbox:    Pointer to the mailbox controller.
>> + *
>> + * The controller driver registers its communication channels
>> + */
>> +int mbox_controller_register(struct mbox_controller *mbox)
>> +{
>> +     int i, txdone;
>> +
>> +     /* Sanity check */
>> +     if (!mbox || !mbox->dev || !mbox->ops || !mbox->num_chans)
>> +             return -EINVAL;
>> +
>> +     if (mbox->txdone_irq)
>> +             txdone = TXDONE_BY_IRQ;
>> +     else if (mbox->txdone_poll)
>> +             txdone = TXDONE_BY_POLL;
>> +     else /* It has to be ACK then */
>> +             txdone = TXDONE_BY_ACK;
>> +
>> +     if (txdone == TXDONE_BY_POLL) {
>> +             mbox->poll.function = &poll_txdone;
>> +             mbox->poll.data = (unsigned long)mbox;
>> +             init_timer(&mbox->poll);
>> +     }
>
> Can't you put this in the statement above?
>
This looked cleaner.

>> +     for (i = 0; i < mbox->num_chans; i++) {
>> +             struct mbox_chan *chan = &mbox->chans[i];
>> +
>> +             chan->cl = NULL;
>> +             chan->mbox = mbox;
>> +             chan->txdone_method = txdone;
>> +             spin_lock_init(&chan->lock);
>> +     }
>> +
>> +     if (!mbox->of_xlate)
>> +             mbox->of_xlate = of_mbox_index_xlate;
>> +
>> +     mutex_lock(&con_mutex);
>> +     list_add_tail(&mbox->node, &mbox_cons);
>> +     mutex_unlock(&con_mutex);
>> +
>> +     return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(mbox_controller_register);
>> +
>> +/**
>> + * mbox_controller_unregister - Unregister the mailbox controller
>> + * @mbox:    Pointer to the mailbox controller.
>> + */
>> +void mbox_controller_unregister(struct mbox_controller *mbox)
>> +{
>> +     int i;
>> +
>> +     if (!mbox)
>> +             return;
>> +
>> +     mutex_lock(&con_mutex);
>> +
>> +     list_del(&mbox->node);
>> +
>> +     for (i = 0; i < mbox->num_chans; i++)
>> +             mbox_free_channel(&mbox->chans[i]);
>> +
>> +     if (mbox->txdone_poll)
>> +             del_timer_sync(&mbox->poll);
>> +
>> +     mutex_unlock(&con_mutex);
>> +}
>> +EXPORT_SYMBOL_GPL(mbox_controller_unregister);
>> diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
>> new file mode 100644
>> index 0000000..0f8cba6
>> --- /dev/null
>> +++ b/include/linux/mailbox_client.h
>> @@ -0,0 +1,45 @@
>> +/*
>> + * Copyright (C) 2013-2014 Linaro Ltd.
>> + * Author: Jassi Brar <jassisinghbrar@...il.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#ifndef __MAILBOX_CLIENT_H
>> +#define __MAILBOX_CLIENT_H
>> +
>> +#include <linux/of.h>
>
> device.h
>
>> +struct mbox_chan;
>> +
>> +/**
>> + * struct mbox_client - User of a mailbox
>> + * @dev:             The client device
>> + * @tx_block:                If the mbox_send_message should block until data is
>> + *                   transmitted.
>> + * @tx_tout:         Max block period in ms before TX is assumed failure
>> + * @knows_txdone:    If the client could run the TX state machine. Usually
>> + *                   if the client receives some ACK packet for transmission.
>> + *                   Unused if the controller already has TX_Done/RTR IRQ.
>> + * @rx_callback:     Atomic callback to provide client the data received
>> + * @tx_done:         Atomic callback to tell client of data transmission
>> + */
>> +struct mbox_client {
>> +     struct device *dev;
>> +     bool tx_block;
>> +     unsigned long tx_tout;
>> +     bool knows_txdone;
>> +
>> +     void (*rx_callback)(struct mbox_client *cl, void *mssg);
>> +     void (*tx_done)(struct mbox_client *cl, void *mssg, int r);
>> +};
>> +
>> +struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
>> +int mbox_send_message(struct mbox_chan *chan, void *mssg);
>> +void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
>> +bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */
>> +void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
>> +
>> +#endif /* __MAILBOX_CLIENT_H */
>> diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
>> new file mode 100644
>> index 0000000..976c4ed
>> --- /dev/null
>> +++ b/include/linux/mailbox_controller.h
>> @@ -0,0 +1,131 @@
>> +/*
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#ifndef __MAILBOX_CONTROLLER_H
>> +#define __MAILBOX_CONTROLLER_H
>> +
>> +#include <linux/of.h>
>
> completion.h
> device.h
> timer.h
>
> Etc.
>
And what else? :)

Cheers,
-jassi
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