Re: [PATCH 7/8] mailbox: f_mhu: add driver for Fujitsu MHU controller

On 17 July 2014 16:01, Sudeep Holla [off-list ref] wrote:

On 17/07/14 07:25, Jassi Brar wrote:

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+       u32 val;
+
+       pr_debug("%s:%d\n", __func__, __LINE__);

Please remove all these debug prints.

These are as good as absent unless DEBUG is defined.

Yes, but with mailbox framework, the controller driver(esp. this one)is
almost like a shim layer. Instead of each driver adding these debugs,
IMO it would be good to have these in the framework.

OK

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+       /* See NOTE_RX_DONE */
+       val = readl_relaxed(mlink->rx_reg + INTR_STAT_OFS);
+       mbox_chan_received_data(chan, (void *)val);
+
+       /*
+        * It is agreed with the remote firmware that the receiver
+        * will clear the STAT register indicating it is ready to
+        * receive next data - NOTE_RX_DONE
+        */

This note could be added as how this mailbox works in general and
it's not just Rx right ? Even Tx done is based on this logic.
Basically the logic is valid on both directions.

Yes that is a protocol level agreement. Different f/w may behave
differently.

Ok, I am not sure if that's entirely true because the MHU spec says it
drives
the signal using a 32-bit register, with all 32 bits logically ORed
together.
Usually only Rx signals are wired to interrupts and Tx needs to be polled
but that's entirely implementation choice I believe.

On my platform, _STAT register only carries the command code but
actual data is exchanged via SharedMemory/SHM. Now we need to know
when the sent data packet (in SHM) has been consumed by the remote -
for which our protocol mandates the remote clear the TX_STAT register.
And vice-versa for RX.

 Some other f/w may choose some other mechanism for TX-Done - say some
ACK bit set or even some time bound guarantee.

More over if it's protocol level agreement it should not belong here :)

My f/w expects the RX_STAT cleared after reading data from SHM. Where
do you think is the right place to clear RX_STAT?

I have said many times in many threads... its the mailbox controller
_and_ the remote f/w that should be seen as one entity. It may not be
possible to write a controller driver that works with any remote
firmware.

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+static int mhu_startup(struct mbox_chan *chan)
+{
+       struct mhu_link *mlink = (struct mhu_link *)chan->con_priv;
+       unsigned long flags;
+       u32 val;
+       int ret;
+
+       pr_debug("%s:%d\n", __func__, __LINE__);
+       spin_lock_irqsave(&mlink->lock, flags);
+       val = readl_relaxed(mlink->tx_reg + INTR_STAT_OFS);
+       writel_relaxed(val, mlink->tx_reg + INTR_CLR_OFS);
+       spin_unlock_irqrestore(&mlink->lock, flags);
+
+       ret = request_irq(mlink->irq, mhu_rx_interrupt,
+                         IRQF_SHARED, "mhu_link", chan);

Just a thought: Can this be threaded_irq instead ?
Can move request_irq to probe instead esp. if threaded_irq ?
That provides some flexibility to client's rx_callback.

This is controller driver, and can not know which client want
rx_callback in hard-irq context and which in thread_fn context.
Otherwise, request_irq() does evaluate to request_threaded_irq(), if
thats what you mean.

Agreed but on contrary since MHU involves external firmware(running
on different processor) which might have it's own latency, I prefer
threaded over hard irq. And yes request_irq does evaluate to
request_threaded_irq but with thread_fn = NULL which is not what I want.

If remote has its own latency, that does not mean we add some more :)

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  There might be use-cases like (diagnostic or other) data transfer
over mailbox where we don't wanna increase latency, so we have to
provide a rx_callback in hard-irq context.

OK

Cool.

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+       for (i = 0; i < 3; i++) {
+               mhu->chan[i].con_priv = &mhu->mlink[i];
+               spin_lock_init(&mhu->mlink[i].lock);
+               res = platform_get_resource(pdev, IORESOURCE_IRQ, i);
+               mhu->mlink[i].irq = res->start;
+               mhu->mlink[i].rx_reg = mhu->base + mhu_reg[i];
+               mhu->mlink[i].tx_reg = mhu->mlink[i].rx_reg + 0x100;
+       }
+
+       mhu->mbox.dev = &pdev->dev;
+       mhu->mbox.chans = &mhu->chan[0];
+       mhu->mbox.num_chans = 3;

Change this to 2, we shouldn't expose secular channel here as Linux can't
access that anyway.

On the contrary, I think the device driver code should be able to
manage every resource - secure or non-secure. If we remove secure
channel option, what do we do on some other platform that needs it?
And Linux may not always run in non-secure mode.

In general secure accesses are avoided these days in Linux as we have no
way to identify it. I agree there are few place where we do access.
Even though I don't like you have secure channel access in Linux, you
have valid reasons. In case you decide to support it, there is some
restrictions in bit 31, though RAZ/WI you need to notify that to protocol
if it tries to access it ?

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  So here we populate all channels and let the clients knows which
channel to use via platform specific details - DT. Please note the
driver doesn't touch any secure resource if client doesn't ask it to
(except SCFG for now, which I think should have some S vs NS DT
binding).

Not sure of this though. We need feedback from DT maintainers.

Yup.


Cheers,
Jassi
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