[PATCH 2/4] dt-bindings: arm: fsl: add mu binding doc

Hi Rob,

Thanks for the review.

-----Original Message-----
From: Rob Herring [mailto:robh at kernel.org]
Sent: Tuesday, May 1, 2018 11:26 PM
To: A.s. Dong <aisheng.dong@nxp.com>
Cc: linux-arm-kernel at lists.infradead.org; dongas86 at gmail.com;
kernel at pengutronix.de; shawnguo at kernel.org; Fabio Estevam
[off-list ref]; dl-linux-imx [off-list ref]; Mark
Rutland [off-list ref]; devicetree at vger.kernel.org
Subject: Re: [PATCH 2/4] dt-bindings: arm: fsl: add mu binding doc

On Sat, Apr 28, 2018 at 02:46:14AM +0800, Dong Aisheng wrote:

quoted

The Messaging Unit module enables two processors within the SoC to
communicate and coordinate by passing messages (e.g. data, status and
control) through the MU interface.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree at vger.kernel.org
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
---
 .../devicetree/bindings/arm/freescale/fsl,mu.txt   | 33

++++++++++++++++++++++

bindings/mailbox/ ?

Why aren't you using the mailbox binding?

It's mainly because MU is not implemented as a mailbox driver,
Instead, they're provided in library calls to gain higher efficiency.

For this case, do i still need to change to mailbox binding?

BTW i.MX MU has only one channel. But the binding doc claims
#mbox-cells must be at least 1. That means the index cells is meaningless
to i.MX MUs.
(Probably mailbox binding could be extended to cover this case?
 E.g. #mbox-cells = <0>)

quoted

 1 file changed, 33 insertions(+)
 create mode 100644
Documentation/devicetree/bindings/arm/freescale/fsl,mu.txt

diff --git
a/Documentation/devicetree/bindings/arm/freescale/fsl,mu.txt
b/Documentation/devicetree/bindings/arm/freescale/fsl,mu.txt
new file mode 100644
index 0000000..a7ceb1f

--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/freescale/fsl,mu.txt

@@ -0,0 +1,33 @@
+NXP i.MX Messaging Unit (MU)
+--------------------------------------------------------------------
+
+The Messaging Unit module enables two processors within the SoC to
+communicate and coordinate by passing messages (e.g. data, status and
+control) through the MU interface. The MU also provides the ability
+for one processor to signal the other processor using interrupts.
+
+Because the MU manages the messaging between processors, the MU

uses

quoted

+different clocks (from each side of the different peripheral buses).
+Therefore, the MU must synchronize the accesses from one side to the
+other. The MU accomplishes synchronization using two sets of matching
+registers (Processor A-facing, Processor Bfacing).

B-facing

Got it

quoted

+
+Messaging Unit Device Node:
+=============================
+
+Required properties:
+-------------------
+- compatible :	should be "fsl,<chip>-mu", the supported chips

include

quoted

+		imx6sx, imx7d, imx7ulp, imx8qxp, imx8qm, imx8mq.

'qm' and 'mq' are really both parts?

Yes, they're two SoCs.

quoted

+- reg :		Should contain the registers location and length
+- interrupts :	Interrupt number. The interrupt specifier format

depends

quoted

+		on the interrupt controller parent.
+
+Examples:
+--------
+lsio_mu0: mu at 5d1b0000 {
+	compatible = "fsl,imx8qxp-mu", "fsl,imx6sx-mu";

It is not clear from the definition above that fsl,imx6sx-mu is a fallback. Is that
true for all the other chips too?

Mx6sx is the first one introducing MU while all others chips are almost using the
same one except MX7ULP with a bit differences.

quoted

+	reg = <0x0 0x5d1b0000 0x0 0x10000>;

Really has 64KB of registers? You are just wasting virtual address space which
is scarce on 32-bit processors with GBs of RAM.

For 32-bit processors, it's 16KB.
For 64-bit processors, yes, according to RM, it's 64KB one slot in the memory
map chapter. But actually It has only 10 registers for user to access,
do you think we need to reduce to the real register size?

quoted

+	interrupts = <GIC_SPI 176 IRQ_TYPE_LEVEL_HIGH>;
+	status = "okay";

Don't show status in examples.

Got it.

Regards
Dong Aisheng

quoted

+};
--
2.7.4

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quoted

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