On 2021-08-19 14:52, Nicolas Frattaroli wrote:
On Donnerstag, 19. August 2021 14:08:36 CEST Robin Murphy wrote:
On 2021-08-17 11:11, Nicolas Frattaroli wrote:
+ rockchip,trcm-sync:
+ $ref: /schemas/types.yaml#/definitions/uint32
+ description:
+ Which lrck/bclk clocks each direction will sync to. You should use
the + constants in <dt-bindings/sound/rockchip,i2s-tdm.h>
+ oneOf:
+ - const: 0
+ description:
+ RK_TRCM_TXRX. Use both the TX and the RX clock for TX and RX.
+ - const: 1
+ description:
+ RK_TRCM_TX. Use only the TX clock for TX and RX.
+ - const: 2
+ description:
+ RK_TRCM_RX. Use only the RX clock for TX and RX.
I wonder if that might make sense to have boolean properties to describe
the latter two cases (which would effectively be mutually-exclusive),
rather than a magic number? Or possibly even just make the respective
clocks optional, if this is something which would be done per-SoC rather
than per-board?
From what I know from downstream vendor device trees, these are per
board, not for the SoC as a whole. There are I2S/TDM controllers on the
SoC which I think are hardwired to certain other IP blocks, such as I2S0
being connected to HDMI, but I2S1 can be routed outside of the SoC where
these come into play I believe.
That's fair enough. I know a lot more about DT bindings than I do about
I2S, but I did guess it might be related to clocking requirements of the
connected codec rather than a constraint of the I2S block itself.
As for making them boolean properties, I'd rather not. If I were to make it
two mutually exclusive booleans, this would result in 4 possible states
rather than 3, and require complexity to check it both in the schema and
in the probe function. Like this, I can get away with a switch case that
has a fallthrough, and a list of consts in the schema.
Complexity?
if (of_property_read_bool(node, "rockchip,trcm-sync-tx-only"))
i2s_tdm->clk_trcm = RK_TRCM_TX;
if (of_property_read_bool(node, "rockchip,trcm-sync-rx-only")) {
if (i2s_td->clk_trcm) {
dev_err(i2s_tdm->dev, "invalid trcm-sync configuration\n");
return -EINVAL;
}
i2s_tdm->clk_trcm = RK_TRCM_RX;
}
if (i2s_td->clk_trcm)
i2s_tdm_dai.symmetric_rate = 1;
If I'm counting correctly, that off-the-top-of-my-head example is a mere
58% of the size of your switch statement ;)
The usual aim in designing bindings to robustly abstract the underlying
features, not to be easy to implement. That's why the "put this magic
value in this register" style of property is generally frowned upon.
As for the schema, it doesn't necessarily have to try to exhaustively
catch every possible usage error - if a combination of properties is so
obviously nonsensical that a driver shouldn't accept it anyway, I'd
imagine it's unlikely to slip through testing.
+
+ "#sound-dai-cells":
+ const: 0
+
+ rockchip,no-dmaengine:
+ description:
+ If present, driver will not register a pcm dmaengine, only the dai.
+ If the dai is part of multi-dais, the property should be present.
+ type: boolean
That sounds a lot more like a policy decision specific to the Linux
driver implementation, than something which really belongs in DT as a
description of the platform.
I agree. Should I be refactoring this into a module parameter or
something along those lines? I'm unsure of where this goes.
Depends on what it actually means, and whether that's something the
driver can figure out for itself. I just see a DT property based around
a particular Linux API call as a big red flag :)
+
+ rockchip,playback-only:
+ description: Specify that the controller only has playback
capability.
+ type: boolean
+
+ rockchip,capture-only:
+ description: Specify that the controller only has capture capability.
+ type: boolean
Could those be inferred from the compatible string, or are there cases
where you have multiple instances of the IP block in different
configurations within the same SoC? (Or if it's merely reflecting
whether the respective interface is actually wired up externally, could
that be inferred from the attached codec?)
Robin.
They can't be inferred from the SoC because there are indeed multiple
instances of this IP block in different configurations on the same SoC.
The RK3566 and RK3568 have four in total, of two different categories,
each being able to be configured for a different format (though the
number of channels and available formats vary for the two categories,
one group only supports I2S and PCM with two channels)
The particular configuration may even vary per-board; an I2S/TDM
controller may be connected to an external codec which does not
support capture, whereas on another board it may be connected to
one that does.
Fair enough again, but surely if the codec doesn't support capture then
in the end no capture interface is going to be exposed anyway - does the
low-level transport need to care?
As an example, if I understand it correctly, I2S3 on the RK3566 and
RK3568 can do 2 channels RX and TX in I2S mode, but only 2 channels
either RX or TX in PCM mode, but I'm unsure of the language in the
(still not public) documentation I have.
And that starts to sound like something the driver should probably be
aware of anyway, but at very least only casts more doubt on these
particular properties - even if an interface to a stereo PCM codec
couldn't support simultaneous playback and recording, couldn't it still
support doing either, separately?
Robin.
