On 23 August 2018 at 10:48, Masahiro Yamada
[off-list ref] wrote:

Hi Jassi,


2018-08-21 19:44 GMT+09:00 Jassi Brar [off-list ref]:

quoted

On 21 August 2018 at 15:17, Masahiro Yamada
[off-list ref] wrote:

quoted

(+CC Rob, DT, LKML)

I forgot to CC this to DT community...


2018-08-21 18:30 GMT+09:00 Masahiro Yamada [off-list ref]:

quoted

The MIO DMAC (Media IO DMA Controller) is used in UniPhier LD4,
Pro4, and sLD8 SoCs.

Signed-off-by: Masahiro Yamada <redacted>
---

 .../devicetree/bindings/dma/uniphier-mio-dmac.txt  | 28 ++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/dma/uniphier-mio-dmac.txt

diff --git a/Documentation/devicetree/bindings/dma/uniphier-mio-dmac.txt b/Documentation/devicetree/bindings/dma/uniphier-mio-dmac.txt
new file mode 100644
index 0000000..a9e969e
--- /dev/null
+++ b/Documentation/devicetree/bindings/dma/uniphier-mio-dmac.txt

@@ -0,0 +1,28 @@
+UniPhier Media IO DMA controller
+
+This works as an external DMA engine for SD/eMMC controllers etc.
+found in UniPhier LD4, Pro4, sLD8 SoCs.
+
+Required properties:
+- compatible: should be "socionext,uniphier-mio-dmac".
+- reg: offset and length of the register set for the device.
+- interrupts: a list of interrupt specifiers associated with the DMA channels.
+- clocks: a single clock specifier
+- #dma-cells: should be <1>. The single cell represents the channel number.
+- dma-channels: specify the number of the DMA channels. This should match to
+  the number of tuples in the interrupts property.
+

Can we not infer the number of channels from interrupt tuples? After
all the driver assumes they are same.

It would be possible to count the number of tuples
in "interrupts".



I know of_irq_count(), but I do not see any driver
in drivers/dma/ that calls it.


I guess the reason is that of_irq_count() is not exported,
so tristate drivers like this cannot use it.


I checked Documentation/devicetree/bindings/dma/,
and some controllers specify _redundant_ dma-channels property.

fsl-mxs-dma.txt
renesas,rcar-dmac.txt
renesas,usb-dmac.txt

:) I am not sure "because others are doing it" is a good reason to
introduce redundancy.

I also see counter-implementation.


bcm2835-dma.c hard-codes the number of channels in the driver.
tegra210-adma.c associates nr_channels with compatible string.



I will wait for comments from the maintainers.

If desired, I will export of_irq_count()
and use it from my driver.

If you don't want to leave too much footprint, you could do

  count = 0;
  while (of_irq_parse_one(dev, count, &irq) == 0) count++

of_irq_parse_one() is already exported.

A good side-effect is you wouldn't have to hardcode the count in the
driver (like bcm and tegra examples you quote).

Having said that, I wouldn't lose sleep over it. So ....

Cheers!