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Message-ID: <20150723082934.GW3061@x1>
Date: Thu, 23 Jul 2015 09:29:34 +0100
From: Lee Jones <lee.jones@...aro.org>
To: Jassi Brar <jassisinghbrar@...il.com>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
kernel@...inux.com, Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/6] mailbox: Add support for ST's Mailbox IP
Let's carry on the conversation here, rather than submitting my fixed
up patch. Once agreed, I will re-send.
> On Fri, Jul 17, 2015 at 5:34 PM, Lee Jones <lee.jones@...aro.org> wrote:
> > ST's platforms currently support a maximum of 5 Mailboxes, one for
> > each of the supported co-processors situated on the platform. Each
> > Mailbox is divided up into 4 instances which consist of 32 channels.
> > Messages are passed between the application and co-processors using
> > shared memory areas. It is the Client's responsibility to manage
> > these areas.
> >
> Thanks. It's a lot better than the old driver. However a few nits as usual :)
>
> > +
> > +#define STI_MBOX_INST_MAX 4 /* RAM saving: Max supported instances */
> >
> Above you say 5 instances. Another u32 doesn't cost much.
This should stay the same. There are 4 instances.
> > +#define STI_MBOX_CHAN_MAX 20 /* RAM saving: Max supported channels */
> > +
> This assumption is reasonable.
>
> > +
> > +static void sti_mbox_enable_channel(struct mbox_chan *chan)
> > +{
> > + struct sti_channel *chan_info = chan->con_priv;
> > + struct sti_mbox_device *mdev = chan_info->mdev;
> > + struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
> > + unsigned int instance = chan_info->instance;
> > + unsigned int channel = chan_info->channel;
> > + unsigned long flags;
> > + void __iomem *base;
> > +
> > + base = mdev->base + (instance * sizeof(u32));
> > +
> Maybe have something simpler like MBOX_BASE(instance)? Or some inline
> function to avoid this 5-lines ritual?
I've checked and we can't do this, as the we need most (all?) of the
intermediary variables too. No ritual just to get the final variable
for instance.
> > + spin_lock_irqsave(&sti_mbox_chan_lock, flags);
> > + mdev->enabled[instance] |= BIT(channel);
> > + writel_relaxed(BIT(channel), base + pdata->ena_set);
> > + spin_unlock_irqrestore(&sti_mbox_chan_lock, flags);
> >
> You don't need locking for SET/CLR type registers which are meant for
> when they could be accessed by processors that can not share a lock.
> So maybe drop the lock here and elsewhere.
>From what I can gather, I think we need this locking. What happens if
we get scheduled between setting the enabled bit in our cache and
actually setting the ena_set bit? We would be out of sync.
> However, you need some mechanism to check if you succeeded 'owning'
> the channel by reading back what you write to own the channel (not
> sure which is that register here). Usually we need that action and
> verification when we assign a channel to some user.
I don't think we need to do that with this driver. All of the
allocation is controlled from within this code base. The channels are
pre-allocated and written into the co-proc's Firmware.
> > +static int sti_mbox_send_data(struct mbox_chan *chan, void *data)
> > +{
> > + struct sti_channel *chan_info = chan->con_priv;
> > + struct sti_mbox_device *mdev = chan_info->mdev;
> > + struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
> > + unsigned int instance = chan_info->instance;
> > + unsigned int channel = chan_info->channel;
> > + void __iomem *base;
> > +
> > + if (!sti_mbox_tx_is_ready(chan))
> > + return -EBUSY;
> This is the first thing I look out for in every new driver :) this
> check is unnecessary.
I see what you mean now. I will remove this check.
> > +static void sti_mbox_shutdown_chan(struct mbox_chan *chan)
> > +{
> > + struct sti_channel *chan_info = chan->con_priv;
> > + struct mbox_controller *mbox = chan_info->mdev->mbox;
> > + int i;
> > +
> > + for (i = 0; i < mbox->num_chans; i++)
> > + if (chan == &mbox->chans[i])
> > + break;
> > +
> > + if (mbox->num_chans == i) {
> > + dev_warn(mbox->dev, "Request to free non-existent channel\n");
> > + return;
> > + }
> > +
> > + sti_mbox_disable_channel(chan);
> > + sti_mbox_clear_irq(chan);
> > +
> > + /* Reset channel */
> > + memset(chan, 0, sizeof(*chan));
> > + chan->mbox = mbox;
> > + chan->txdone_method = TXDONE_BY_POLL;
> >
> No please. mbox_chan is owned by the API. At most you could clear con_priv.
Removed.
> > +static struct mbox_chan *sti_mbox_xlate(struct mbox_controller *mbox,
> > + const struct of_phandle_args *spec)
> > +{
> > + struct sti_mbox_device *mdev = dev_get_drvdata(mbox->dev);
> > + struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
> > + struct sti_channel *chan_info;
> > + struct mbox_chan *chan = NULL;
> > + unsigned int instance = spec->args[0];
> > + unsigned int channel = spec->args[1];
> > + unsigned int direction = spec->args[2];
> > + int i;
> > +
> > + /* Bounds checking */
> > + if (instance >= pdata->num_inst || channel >= pdata->num_chan) {
> > + dev_err(mbox->dev,
> > + "Invalid channel requested instance: %d channel: %d\n",
> > + instance, channel);
> > + return NULL;
> > + }
> > +
> > + for (i = 0; i < mbox->num_chans; i++) {
> > + chan_info = mbox->chans[i].con_priv;
> > +
> > + /* Is requested channel free? */
> > + if (direction != MBOX_LOOPBACK &&
> > + chan_info &&
> > + mbox->dev == chan_info->mdev->dev &&
> > + instance == chan_info->instance &&
> > + channel == chan_info->channel) {
> > + dev_err(mbox->dev, "Channel in use\n");
> > + return NULL;
> > + }
> > +
> > + /* Find the first free slot */
> > + if (!chan && !chan_info)
> > + chan = &mbox->chans[i];
> shouldn't it break out of loop here?
I checked that and we don't. We need to check all of the channels do
wee if we have double allocated. If we have, NULL is returned from
above.
I have; however, updated the comment above for clarity.
> > + }
> > +
> Doesn't mbox->chans[i].con_priv need some locking here?
Not that I can see. Would you mind explaining further please?
> > +static const struct sti_mbox_pdata mbox_stih407_pdata = {
> > + .num_inst = 4,
> > + .num_chan = 32,
> > + .irq_val = 0x04,
> > + .irq_set = 0x24,
> > + .irq_clr = 0x44,
> > + .ena_val = 0x64,
> > + .ena_set = 0x84,
> > + .ena_clr = 0xa4,
> >
> Register offsets are parameters of the controller, and also these look
> ugly. Please make these #define's
These are now #defined.
> > +static int __init sti_mbox_init(void)
> > +{
> > + return platform_driver_register(&sti_mbox_driver);
> > +}
> > +
> > +static void __exit sti_mbox_exit(void)
> > +{
> > + platform_driver_unregister(&sti_mbox_driver);
> > +}
> > +
> > +postcore_initcall(sti_mbox_init);
> >
> This seems fragile. Shouldn't the users defer probe if they don't get a channel?
This has been converted to module_platform_driver()
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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